The effect of ammonia concentration ranging from 0 to 10 g NIL on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate at 35 degrees C and initial pH 7.0. The experimental results showed that during the fermentative hydrogen production, the substrate degradation efficiency increased with increasing ammonia concentration from 0 to 0.01 g NIL The hydrogen production potential, hydrogen yield and average hydrogen production rate increased with increasing ammonia concentration from 0 to 0.1 g N/L. The maximum hydrogen production potential of 291.4 mL, maximum hydrogen yield of 298.8 mL/g glucose and maximum average hydrogen production rate of 8.5 mL/h were all obtained at the ammonia concentration of 0.1 g N/L. (C) 2008 Elsevier Ltd. All rights reserved.