It has been reported that the pretreatment of lignocellulosic materials to remove lignin or hemicelluloses has significantly improved the hydrolysis process of the biochemical conversion. However, the pretreatment process should meet some important features which include, avoiding the formation of byproducts that can be potential inhibitors for the subsequent hydrolysis and fermentation processes. Switchgrass has been identified as a good lignocellulosic candidate for the production of cellulosic ethanol. Dilute acid pretreatment of switchgrass, followed by enzymatic hydrolysis solubilizes the monosaccharides, which can then be fermented into biofuels.  A high yield of xylose recovery is important for the economic aspect of cellulosic ethanol production because hemicellulose, which is converted to xylose, accounts for up to a third of the total carbohydrate in this lignocellulosic material. Unfortunately, pretreatment leads to the formation of inhibitors, which deter the fermentation step. The objectives of this research were to determine the cytotoxicity of pretreated switchgrass extracts, both before and after neutralization with calcium carbonate.  Yellow MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based assays of these extracts were used to determine if these compounds were toxic to the immortal cervical cancer cell line of Helen Lane (HeLa). Data was recorded and analyzed by Microsoft Excel or JMP 6.0.  The findings of these studies are being analyzed for determining the biological activity of these pretreatment extracts of switchgrass.     The long term goal of this research is aimed at identifying groups of compounds that are formed during pretreatment and that inhibit the fermentation.