DELAFIELD, Wis. (Stockpickr) -- Corporate insiders sell their own companies' stock for a number of reasons.

They might need the cash for a big personal purchase such as a new house or yacht, or they might need the cash to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price.

Other times they sell because they think their stock is overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share.

But insiders usually buy their own shares for one reason: They think the stock is a bargain and has tremendous upside.

The key word in that last statement is "think." Just because a corporate insider thinks his or her stock is going to trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

Recently, a number of companies' corporate insiders have bought large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks.

Mirati Therapeutics

One biopharmaceutical player that insiders are jumping into here is Mirati Therapeutics (MRTX - Get Report) , which is engaged in the development and commercialization of therapeutics for cancer and fungal diseases. Insiders are buying this stock into strength, since shares have trended higher by 24% over the last six months.

Mirati Therapeutics has a market cap of $286 million and an enterprise value of $246 million. This stock trades at a premium valuation, with a price-to-book of 7.94. Its estimated growth rate for this year is 29.6%, and for next year it's pegged at -10.3%. This is a cash-rich company, since the total cash position on its balance sheet is $37.71 million and its total debt is zero.

A beneficial owner just bought 425,000 shares, or about $8.5 million worth of stock, at $20 per share. Another beneficial owner also just bought 50,000 shares, or about $1 million worth of stock, at $20 per share.

From a technical perspective, MRTX is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending strong for the last two months, with shares moving higher from its low of $13.68 to its recent high of $22.65 a share. During that uptrend, shares MRTX have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed shares of MRTX within range of triggering a big breakout trade.

If you're bullish on MRTX, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $18.42 a share and then once it breaks out above some key near-term overhead resistance levels at $21.54 to $22.65 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average volume of 47,657 shares. If that breakout triggers soon, then MRTX will set up to re-test or possibly take out its next major overhead resistance levels at $23.75 to its all-time high of $25.97 a share. Any high-volume move above those levels will then give MRTX a chance to tag $30 a share.

Albmarle

A basic materials player that insiders are active in here is Albemarle (ALB - Get Report) , which develops, manufactures and markets engineered specialty chemicals. Insiders are buying this stock into weakness, since shares have dropped by 20% over the last six months.

Albemarle has a market cap of $3.8 billion and an enterprise value of $4.1 billion. This stock trades at a reasonable valuation, with trailing price-to-earnings of 29 and a forward price-to-earnings of 11. Its estimated growth rate for this year is -6.4%, and for next year it's pegged at 14%. This is not a cash-rich company, since the total cash position on its balance sheet is $2.49 billion and its total debt is $2.93 billion. This stock currently sports a dividend yield of 2.3%.

A director just bought 7,847 shares, or about $380,000 worth of stock, at $48.48 per share.

From a technical perspective, ALB is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the month, with shares moving lower from its high of $62.23 a share to its new 52-week low of $46.78 a share. During that downtrend, shares of ALB have been consistently making lower highs and lower lows, which is bearish technical price action. That said, shares of ALB have now started to bounce off that $46.78 low with strong upside volume flows.

If you're in the bull camp on ALB, then I would look for long-biased trades as long as this stock is trending above its new 52-week low of $46.78 a share and then once it takes out Tuesday's intraday high of $49.54 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average action of 1.87 million shares. If that breakout hits soon, then ALB will set up to re-test or possibly take out its next major overhead resistance levels $56 to its 50-day moving average of $58.27 a share.

Microsoft

One technology player that insiders are loading up on here is Microsoft (MSFT - Get Report) , which develops, licenses, markets and supports software, services and devices worldwide. Insiders are buying this stock into notable weakness, since shares have fallen by 12.3% over the last three months.

Microsoft has a market cap of $341 billion and an enterprise value of $277 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 16.7 and a forward price-to-earnings of 14. Its estimated growth rate for this year is -7.2%, and for next year it's pegged at 20.9%. This is a cash-rich company, since the total cash position on its balance sheet is $89.57 billion and its total debt is $28.74 billion.

A director just bought 23,612, or about $999,000 worth of stock, at $42.34 per share.

From a technical perspective, MSFT is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending over the last few weeks, with shares moving lower from its high of $47.39 to its recent low of $40.23 a share. During that downtrend, shares of MSFT have been consistently making lower highs and lower lows, which is bearish technical price action. That said, shares of MSFT have now started to rebound off that $40.23 low and it's now moving within range of triggering a near-term breakout trade.

If you're bullish on MSFT, then I would look for long-biased trades as long as this stock is trending above its recent low of $40.23 a share and then once it breaks out above some near-term overhead resistance levels at $42 to its gap-down-day high of $43.20 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 34.64 million shares. If that breakout develops soon, then MSFT will set up to re-test or possibly take out its next major overhead resistance levels at its 50-day moving average $46.51 to around $47 to $48 a share.

Bank of New York Mellon

One asset management player that insiders are buying up a ton of stock in here is Bank of New York Mellon (BK - Get Report) , which provides various financial products and services in the U.S. and internationally. Insiders are buying this stock into modest weakness, since shares have trended down by just 3.4% over the last six months.

Bank of New York Mellon has a market cap of $41.8 billion and an enterprise value of $67.3 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 14 and a forward price-to-earnings of 12. Its estimated growth rate for this year is 8.8%, and for next year it's pegged at 19.6%. This is a cash-rich company, since the total cash position on its balance sheet is $162 billion and its total debt is $53.70 billion. This stock currently sports a dividend yield of 1.9%.

A director just bought 273,000 shares, or about $9.99 million worth of stock, at $36.63 per share.

From a technical perspective, BK is currently trending below both its 50-day and 200-day moving averages, which is bearish. This stock has been downtrending for the last month and change, with shares moving lower from its high of $41.60 to its recent low of $35.46 a share. During that downtrend shares of BK have been making mostly lower highs and lower lows, which is bearish technical price action. That said, shares of BK have now started to rebound off that $35.46 low and it's beginning to move within range of triggering a near-term breakout trade.

If you're bullish on BK, then I would look for long-biased trades as long as this stock is trending above that recent low of $35.46 and then once it breaks out above its 200-day moving average of $37.47 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average action of 4.91 million shares. If that breakout kicks off soon, then BK will set up to re-test or possibly take out its next major overhead resistance levels at $38.56 to its 50-day moving $39.17 a share, or even $40 to $41 a share.

Alnylam Pharmaceuticals

One final stock with some huge insider buying is Alnylam Pharmaceuticals (ALNY) , which is engaged in discovering, developing and commercializing novel therapeutics based on RNA interference. Insiders are buying this stock into major strength, since shares have soared higher by 65% over the last six months.

Alnylam Pharmaceuticals has a market cap of $6.8 billion and an enterprise value of $6.4 billion. This stock trades at a premium valuation, with a price-to-sales of 189.83 and a price-to-book of 7.82. Its estimated growth rate for this year is -242.1%, and for next year it's pegged at 45.2%. This is a cash-rich company, since the total cash position on its balance sheet is $631.93 million and its total debt is zero.

A beneficial owner just bought 647,448 shares, or about $61.50 million worth of stock, at $95 per share. The CEO also just bought 10,000 shares, or about $950,000 worth of stock, at $95 per share.

From a technical perspective, ALNY is currently trending below its 50-day moving average and above its 200-day moving average, which is neutral trendwise. This stock have recently started to bounce higher right above some near-term support at $85.03 a share. That bounce is beginning to push shares of ALNY within range of triggering a near-term breakout trade above some key near-term overhead resistance levels.

If you're bullish on ALNY, then I would look for long-biased trades as long as this stock is trending above some near-term support at $85.03 a share and then once it breaks out above some key near-term overhead resistance levels at $95 to $96.80 a share and then above its 50-day moving average of $97.38 a share with high volume. Look for a sustained move or close above those levels with volume that registers near or above its three-month average volume of 723,745 shares. If that breakout begins soon, then ALNY will set up to re-test or possibly take out its next major overhead resistance levels at $105 to $108.86 a share.

-- Written by Roberto Pedone in Delafield, Wis.

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At the time of publication, author had no positions in stocks mentioned. Roberto Pedone, based out of Delafield, Wis., is an independent trader who focuses on technical analysis for small- and large-cap stocks, options, futures, commodities and currencies. Roberto studied international business at the Milwaukee School of Engineering, and he spent a year overseas studying business in Lubeck, Germany. His work has appeared on financial outlets including CNBC.com and Forbes.com. You can follow Pedone on Twitter at www.twitter.com/zerosum24 or @zerosum24.