In present study, an electric field was newly adopted as a pretreatment method for inoculum preparation in dark fermentative hydrogen production. Various voltages (5-20 V for 10 min) were applied, and the feasibility and efficiency of this method were compared with those of heat pretreatment (90 degrees C for 20 min). Both the highest H-2 yield, 1.43 mol H-2/mol hexose(added), and the highest production rate, 101.4 mL H-2/L/h, were observed at 10 V. While RNA concentration of above 100 mg/L was maintained up to 10 V, it was decreased at an applied voltage of 20 V, where the worst performance was observed. Microbial analysis results confirmed that only H-2 producing bacteria were detected with electric pretreatment, while non-H-2 producing bacteria coexist with heat and electric (5 V) pretreatment. The results suggested that application of an electric field has reasonable potential as an alternative method for preparing inoculums for hydrogen production. (c) 2013 Elsevier Ltd. All rights reserved.