Toxicity renders certain industrial effluents unfit for recovering its bioenergy content. An enriched single strain, Clostridium butyricum, was herein applied to fermentatively produce hydrogen from glucose in the presence of 200-1500 mg L(-1) of phenol. The enriched C. butyricum yielded hydrogen at approximately 1.4 mol H(2) mol(-1) glucose in the presence of 200-400 mg L(-1) phenol. Significant inhibition of cell metabolism was noted at phenol concentration >1000 mg L(-1). During glucose fermentation, phenol dosed at 200-400 mg L(-1) was partly co-degraded. Ethanol and acetate were the primary metabolites, whose yields increased with increasing phenol concentration. The present results revealed the potential to harvest hydrogen from a toxic (phenol-containing) wastewater. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.