During pretreatment and hydrolysis of fiber-rich agricultural biomass, compounds such as salts, furfural, hydroxymethyl furfural (HMF), acetic, ferulic, glucuronic, ρ-coumaric acids, and phenolic compounds are produced. Clostridium beijerinckii BA101 can utilize the individual sugars present in lignocellulosic [e.g., corn fiber, distillers dry grain solubles (DDGS), etc] hydrolysates such as cellobiose, glucose, mannose, arabinose, and xylose. In these studies we investigated the effect of some of the lignocellulosic hydrolysate inhibitors associated with C. beijerinckii BA101 growth and acetone–butanol–ethanol (ABE) production. When 0.3 g/L ρ-coumaric and ferulic acids were introduced into the fermentation medium, growth and ABE production by C. beijerinckii BA101 decreased significantly. Furfural and HMF are not inhibitory to C. beijerinckii BA101; rather they have stimulatory effect on the growth of the microorganism and ABE production. Biotechnol. Bioeng. 2007;97:1460–1469. © 2007 Wiley Periodicals, Inc.