The toxicity of several compounds commonly found in lignin hydrolysates were evaluated individually by monitoring the production of acetone, butanol, and ethanol (ABE) from Clostridium beijerinckii. The compounds selected for analysis included coumaric acid, syringaldehyde, furfural, ferulic acid and glucuronic acid. Very significant losses in butanol and acetone production were evident when the cultures were exposed to 0.5 mg/mL coumaric or ferulic acid, with a concurrent increase in the amount of acetic acid and butyric acid being produced. Exposure to syringaldehyde led a reduced butanol production while the addition of up to 1 mg/mL of furfural or glucuronic acid had little or no effect on the metabolic output of this strain. To further evaluate, and potentially identify, the stresses C. beijerinckii experience when exposed to each of these compounds, tests were performed using a panel of bioluminescent strains of E. coli. The stresses experienced when bacteria were exposed to each compound were characterized based upon the bioluminescent responses from these strains. Syringaldehyde led to a significant amount of membrane damage, with the bioluminescent response from strain DPD2540 being induced more than 400-fold when syringaldehyde was added to a concentration of 1 mg/mL. This is an abstract of a paper presented at the 2008 AIChE Spring National Meeting (New Orleans, LA 4/6-10/2008).