The toxicity of oak and yellow-poplar wood extracts, as well as a first-stage hardwood hydrolyzate liquor prepared from a red oak:white oak:yellow-poplar (1:1:1) sawdust, on Saccharomyces cerevisiae D5A was examined. Acetone/water and hot methanol extracts of solid biomass samples from white oak, red oak, and yellow-poplar gave 88-94% of the ethanol produced with controls. The organism was tolerant to the compounds present in the xylose-rich hydrolyzate, with fermentation efficiency being improved to 97% of that obtained with controls by using an overliming/thermal conditioning protocol.