Each business day, TheStreet.com Ratings compiles a list of the top five stocks in five categories -- fast-growth, all-around value, large-cap, mid-cap and small-cap -- and publishes these lists in the Ratings section of our Web site.

This list is based on data from the close of the previous trading session. Today we focus on mid-caps. These are stocks of companies that have market capitalizations of between $500 million and $10 billion that rank near the top of all stocks rated by our proprietary quantitative model, which looks at more than 60 factors.

The stocks must also be followed by at least one financial analyst who posts estimates on the Institutional Brokers' Estimate System. They are ordered by their potential to appreciate.

Note that no provision is made for off-balance-sheet assets such as unrealized appreciation/depreciation of investments, market value of real estate or contingent liabilities that might affect book value. This could be material for some companies with large underfunded pension plans.

Circor International ( CIR) has been manufacturing an array of valves since the early 1900s. Valves range in application from generic products for heating and cooling to more specialized steam catapult valves on nuclear-powered aircraft carriers and cryogenic valves used in the space shuttle.

Circor has been rated a buy since November 2004. The company's strengths can be seen in multiple areas, such as its impressive record of earnings per share growth, compelling growth in net income, revenue growth and solid stock price performance. Earnings per share grew 68.9% for the first quarter of fiscal year 2008 when compared with the same quarter of fiscal 2007, which brought its three year average EPS growth rate to a solid 47.7%. The company reported 9.5% growth in its revenue over the same period, which trailed its industry average but allowed it to boost net income, which grew 74.1% for the interim. In addition, as of the market's close on May 20th of this year, Circor's share price has jumped 38.8% compared with its closing price of one year prior. The stock currently trades at a valuation level that is in line with its peer average and a discount to the S&P 500 average.

We feel that the company's strengths outweigh the fact that Circor sports a relatively low operating profit margin, at 11.1% for the quarter just ended. In its release reporting first quarter results, the company indicated that its orders grew 27% year over year on the back of strength in its naval, aerospace and energy markets. Its backlog jumped 45% from the year-ago quarter. Management is guiding investors to expect EPS for the second quarter in the range of 74 cents to 83 cents, excluding special charges. This compares with 60 cents earned for the second quarter of fiscal 2007.

Sigma-Aldrich ( SIAL) develops, manufactures and distributes a broad range of quality biochemicals and organic chemicals. These chemical products and kits are used in scientific and genomic research, biotechnology, pharmaceutical development and the diagnosis of disease.

Our buy rating for Sigma-Aldrich has been in place since November 2003. For the second quarter of fiscal 2008, the company reported revenue growth of 14.4% year over year. This growth appears to have trickled down to the bottom line, as earnings per share (EPS) improved 16.7% compared with the same quarter of fiscal 2007, rising from 60 cents per share to 70 cents per share. Net income rose from $79.90 million in the second quarter of fiscal 2007 to $90.80 million in the most-recent quarter, while net operating cash flow significantly increased, rising 77.24% to $1.32 billion. Additionally, a low debt-to-equity ratio of 0.37 implies that the company has successfully managed it debt levels.

Management announced that it was pleased with the strong growth that Sigma-Aldrich achieved during the second quarter and expects the momentum to carry through the final quarter of fiscal 2008 and allow the company to meet its goal of 7% organic sales growth. Looking ahead, the full-year EPS forecast has been increased to $2.62 to $2.72 per share. However, bear in mind that Sigma-Aldrich's future results could be negatively impacted by changes in pricing due to the competitive environment, fluctuations in foreign currency exchange rates, and regulatory changes.

American Ecology ( ECOL) is one of the nation's oldest providers of radioactive, hazardous and industrial waste management services. The company's customers are commercial and government entities, such as nuclear power plants, medical and academic institutions, steel mills, refineries and chemical production facilities.

We have rated American Ecology a buy since October 2005. The company reported record operating results for the second quarter of fiscal 2008, as operating income rose 20% year over year to $9.8 million. Net income also climbed 20%, reaching $6.1 million compared with $5.1 million in the same quarter one year prior, due to strong growth in disposal service revenue as the Idaho, Nevada, and Texas waste facilities increased the amount of waste disposed by 18% year over year. However, lower transportation revenue partially offset the increase in disposal service revenue. American Ecology also reported a 17% increase in gross profit for the second quarter, and the company had no debt at quarter end. In addition, the company declared a quarterly dividend of 18 cents per common share, which was a 20% increase from the prior quarterly dividend of 15 cents per common share.

Looking ahead, the company announced that it expects to reach or possibly surpass its previously announced fiscal 2008 earnings guidance of $1.17 to $1.23 per diluted share. Management cautioned that the company will require a strong second half contribution from the thermal desorption recycling service that was initiated in late June, along with solid even business results if it is to exceed its guidance range.

Amphenol ( APH) designs, manufactures and markets electrical, electronic and fiber optic connectors, interconnect systems and coaxial and flat-ribbon cable.

Our buy rating for Amphenol has been in place since June 2003. The company reported record EPS growth of 33% year over year for the second quarter of fiscal 2008, along with record sales that rose 23% to $846.8 million. The global communications, military, and commercial aerospace markets performed particularly well for the company, although growth was broad based. Net income for the second quarter rose to $110.00 million from $84.00 million a year ago. During the quarter, Amphenol broadened its technology offering in the military market by completing the acquisition of a U.S. manufacturer of audio interconnect products for that market. Additionally, the company's profitability and cash flow remained strong in the second quarter.

Looking ahead, Amphenol forecasts revenue for the third quarter of fiscal 2008 in the range of $825.00 million to $840.00 million. In addition, EPS is expected to be in the range of 59 cents to 61 cents per share. The company raised its full year 2008 revenue growth guidance to 15.0% to 16.0 % year over year, or $3.28 billion to $3.31 billion. Management reported continued strength in its business despite economic uncertainties and a generally moderate demand in certain markets. However, low profit margins could be a concern, and as could any unfavorable changes, particular in the communication and defense markets that are the company's highest revenue contributors.

Ameron International ( AMN) manufactures highly-engineered products and materials for the chemical, industrial, energy, transportation and infrastructure markets worldwide. The company's products include such items as high-performance coatings and surfacer systems for the preservation of structures, molded fiberglass pipes and fittings, ready-mix concrete, and products and services used in the construction of water pipelines.

Ameron has been rated a buy since June 2005. Strong performances from the Fiberglass-Composite-Pipe Group and TAMCO (Ameron's 50%-owned steel mini-mill) led to higher results in the second quarter of fiscal 2008. The company reported a slight revenue increase of 1.9% year over year, which appears to have helped boost earnings per share (EPS) from $1.63 in the second quarter of fiscal 2007 to $1.78 in the most-recent quarter. Net income increased 3.4% when compared with the same quarter one year prior, rising from $15.80 million to $16.33 million. Return on equity also improved slightly, and the company appears to be successfully managing its debt levels.

Management was overall pleased with the year-to-date results, as the company's performance for the first half of fiscal 2008 was positive. The company anticipates steady returns for the year from its various businesses, with TAMCO and the Fiberglass-Composite-Pipe Group expected to continue performing at record levels. However, weak market conditions will most likely continue to negatively affect the Infrastructure Products Group. Bear in mind that the building products industry's performance is cyclical, depending on the overall health of the U.S. economy. The state of the housing and auto markets in particular could impact this industry and, therefore, this stock.

Our quantitative rating is based on a variety of historical fundamental and pricing data and represents our opinion of a stock's risk-adjusted performance relative to other stocks.

However, the rating does not incorporate all of the factors that can alter a stock's performance. For example, it doesn't always factor in recent corporate or industry events that could impact the stock price, nor does it include recent technology developments and competitive dynamics that may affect the company.

This article was written by a staff member of TheStreet.com Ratings.

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