Tuesday proved a mixed day for small-cap stocks, which opened higher only to fall back down to trade around the baseline as earnings guidance and downgrades brought several stocks lower. Among the winners, RehabCare ( RHB), a St. Louis provider of rehabilitation program management services in hospitals, gained 20% to $16.56 after Stifel Nicolaus upgraded the stock to buy from hold. Also rising, Menlo Park, Calif.'s Exponent ( EXPO), which provides science and engineering consulting services, added 15% to $35.84 after posting a first-quarter earnings beat. Exponent earned $6.3 million, or 40 cents a share, vs. $5.1 million, or 31 cents a share, a year ago. Analysts were expecting EPS of 33 cents. On the losing side, investors took a bite out of Crocs ( CROX), sending the stock down more than 40% to new lows. The shoe maker, based in Niwot, Colo., slashed guidance for the first quarter. Weisel downgraded the stock to market-weight. Shares were falling $7.44, to $10.35. PDF Solutions ( PDFS) also fell on lowered guidance. The San Jose, Calif., provider of yield improvement technologies forecast first-quarter revenue between $20 million and $20.5 million and a non-GAAP loss between a penny and 3 cents a share. Analysts polled by Thomson Financial are looking for EPS of 8 cents on revenue of $23.9 million. Shares, which sank to a new low of $3.86, were recently trading down 29% at $4. Meanwhile, San Diego, Calif., wireless broadband company Novatel ( NVTL) saw shares plummet 22% to $7.81. The company forecast revenue of $91 million and non-GAAP EPS between 16 cents and 18 cents. Analysts are predicting revenue of $110.5 million and EPS of 22 cents. Oppenheimer downgraded the stock to perform from outperform, and Morgan Joseph cut its rating to hold from buy. Shares of Alpharetta, Ga.-based Radiant Systems ( RADS) lost their luster, dropping 17% to $11.62. The developer of solutions for managing site operations for hospitality and retail businesses suffered a Wedbush Morgan downgrade to hold from buy. Finally, CoBiz Financial ( COBZ), a Denver provider of financial products and services in Colorado and Arizona, gave up 13% to $10.30. The company announced it would record a $5 million pretax loan loss provision for the first quarter and will charge off $1.7 million. Keefe Bruyette downgraded Cobiz to market perform from outperform. More broadly, the Russell 2000 was recently losing 0.1% to 685.81, and the S&P SmallCap 600 was largely unchanged at 362.52.