The Standard & Poor's SmallCap 600 Index fell at midday as oil prices approached $130 a barrel and the Labor Department said in a report wholesale inflation rose 0.2 percent last month.
The S&P SmallCap 600 Index lost 1.72 points to 389.56. The index tracks stocks with a market capitalization between $300 million and $2 billion.
Small-cap companies make up about 3 percent of the total U.S. securities market, but are often cited as good investments due to their low valuations and potential to grow into big-cap stocks.
Universal Tech Institute fell $1.31, or 10.1 percent, to $11.61 after a Banc of America analyst downgraded the education provider to "Sell" from "Neutral," saying it has reached a fair price.
Chemical and building supply maker Georgia Gulf Corp. lost 41 cents, or 8.2 percent, to $4.60.
Casey's General Stores lost $1.63, or 7.1 percent, to $21.32. Friedman, Billings, Ramsey analyst Karen Short downgraded the convenience store operator to "Underperform" from "Market Perform" in a note and set a price target nearly 9 percent lower than its last closing price.
Among the gainers, United Natural Foods Inc. jumped $1.94, or 10.6 percent, to $20.21. On Tuesday, the natural and organic food distributor said its third-quarter profit fell 5 percent, but the results still beat analyst estimates.
The Dayville, Conn., company also reaffirmed its full-year outlook.
Metal-based product maker Material Sciences Corp. gained 60 cents, or 8.4 percent, to $7.76.
Rudolph Technologies Inc., climbed 44 cents, or 4.7 percent, to $9.85 after Piper Jaffray's Auguste P. Richard upgraded the company, which makes equipment used in semiconductor manufacturing, to "Buy" from "Neutral," citing its strong position in key markets.