Acetone butanol ethanol (ABE) was produced from hydrolysed corn stover and switchgrass using Clostridium beijerinckii P260. A control experiment using glucose resulted in the production of 21.06 g L-1 total ABE. In this experiment an ABE yield and productivity of 0.41 and 0.31 g L-1 h(-1) was achieved, respectively. Fermentation of untreated corn stover hydrolysate (CSH) exhibited no growth and no ABE production; however, upon dilution with water (two fold) and wheat straw hydrolysate (WSH, ratio 1:1), 16.00 and 18.04 g L-1 ABE was produced, respectively. These experiments resulted in ABE productivity of 0.17-0.21 g L-1 h(-1). Inhibitors present in CSH were removed by treating the hydrolysate with Ca(OH)(2) (overliming). The culture was able to produce 26.27 g L-1 ABE after inhibitor removal. Untreated switchgrass hydrolysate (SGH) was poorly fermented and the culture did not produce more than 1.48 g L-1 ABE which was improved to 14.61 g L-1. It is suggested that biomass pretreatment methods that do not generate inhibitors be investigated. Alternately, cultures resistant to inhibitors and able to produce butanol at high concentrations may be another approach to improve the current process. Published by Elsevier Ltd.