Lignocellulose consists of various components which are released by pretreatment and the actions of cellulolytic enzymes.  In the case of liquid hot water pretreatment (LHW) of lignocellulosic biomass, the preatreatment solubilizes oligomers and acetic acid from hemicellulose and phenolic compounds from both hemicellulose and lignin. The soluble compounds in the liquid fraction of LHW pretreated cellulosic biomass strongly inhibits the cellulolytic activities of enzymes.  In this study, the inhibitory effects of the soluble components in the LHW pretreatment liquid were assessed using pretreated maple and corn stover as a source of inhibitors and Solka Floc as the reactant,  Solka Floc at 1% solids loading was readily hydrolyzed at an enzyme loading of 15 FPU cellulase per g cellulose.  However when inhibitors were introduced by adding pretreatment liquid to the Solka Floc and buffer, the glucose yield after 72 hrs was reduced by 50%.  Among the soluble components in the pretreatment liquid, phenolic compounds were found to be the strongest inhibitors of cellulose hydrolysis. This was further verified by removal of phenolics from the pretreatment liquid which resulted in a significant yield improvement.  The relationship between hydrolysis efficiency and the mass ratio of phenolic compounds to cellulase proteins was also measured.  The mechanisms of cellulase inhibition/deactivation by sugar-oligomers and phenolics were further probed using individual inhibitor molecules.  The combined effects were then studied through simultaneous saccharification and fermentation of Solka Floc and pretreated lignocellulosic substrates.  The results show that phenolics are strong inhibitors whose effects may be moderated  by washing them away from the lignocellulosic substrates.