Biological hydrogen production from the anaerobic fermentation of ultrasonic-pretreated paper mill sludge started at a pH of 5.5 and a temperature of 36.5 degrees C. When the sludge reaction time (SRT) was 32 h, the organic loading rate (OLR) was 3; 000 mg chennai oxygen demand (COD).L-1.d(-1), and the hydrogen production yield was 620: 8 mL H-2/g COD. The Gompertz equation was used for regression analysis of accumulated hydrogen yield, which indicated that R-2 was 0.99. Hydrogen was produced by typical ethanol-type fermentation and the utilization of organic material was 31.8%. DOI: 10.1061/(ASCE)EY.1943-7897.0000054. (C) 2012 American Society of Civil Engineers.