NEW YORK ( TheStreet) -- In the first months of 2010, aiming small has paid off in a big way. Both small- and micro- cap ETFs have managed to handedly beat the broad S&P 500 Index.Typically, investors are attracted to small- and micro-cap companies for their greater growth potential. However, as the size of the companies underlying a fund get smaller, they tend to see wilder swings to the up and downside. For this reason, it makes even more sense to diversify, especially with the smallest of small caps, the microcaps. There are dozens of products available to investors looking for exposure to small-cap firms. However, the options for investors interested in micro-cap ETFs are limited. Currently, only three ETFs bear mention: the iShares Russell Microcap Index Fund ( IWC); the PowerShares Zack's Micro Cap Portfolio ( PZI); and the First Trust Dow Jones Select MicroCap Index Fund ( FDM). IWC is the largest of these three ETF options, with $440 million in assets. Due to the small size of the fund's underlying holdings, IWC does not have any holding which can drive the product's performance. The fund's No. 1 position, Dana Holdings ( DAN), accounts for only 0.7% the total index. Together, IWC's top 10 positions make up less than 5% of the fund. Other top holdings include, Veeco Instruments ( VEC), Arvinmeritor ( ARM), and Dollar Thrifty Automotive Group ( DTG). The largest sectors represented in IWC's portfolio are financial services, technology, health care and consumer discretionary. Together, these four industries account for nearly three quarters of the fund. Financials represent the largest slice, commanding over 23%. IWC carries a 0.68% expense ratio. PZI also has a heavily diversified index. Keryx Biopharmaceuticals ( KERX) is the fund's largest holding, but makes up less than 0.5% of the total index. Other top holdings include RAIT Financial Trust ( RAS), Federal Agricultural Mortgage Corp ( AGM) and Power-One ( PWER). PZI's top 10 positions represent 4% of the fund. Once again, a small number of sectors make up the lion's share of PZI's portfolio. This time, however, it is consumer discretionary, with a 23% slice, making up the largest chunk. Financials, technology and industrials together represent another 50% of the fund. PZI carries a 0.86% expense ratio. With nearly $23 million in assets, FDM is the smallest of the micro-cap ETFs. The fund's three top holdings: EV Energy Partner ( EVEP), ATP Oil & Gas ( ATPG), and Belo ( BLC) each represent 1% of the fund. Together, FDM's top 10 holdings make up over 9% of the fund.