We evaluated the influence of the operation temperature (mesophilic vs. thermophilic regime) of semicontinuous, acidogenic solid substrate anaerobic digestion (A-SSAD) of the organic fraction of municipal solid waste (OFMSW) at lab scale. The H-2 percentage was higher in the thermophilic regime than in the mesophilic operation (58% and 42%, respectively). The H-2 yield of thermophilic A-SSAD was significantly higher than in our mesophilic reactors (360 vs. 165 NmL H-2/9 VSrem) and other studies reported in the literature (range of 62-180mL/g VS). Mesophilic A-SSAD showed a yield of 37% of the maximum yield based on 4 mol H-2/mol hexose, while thermophilic A-SSAD exhibited a yield of 80% of the maximum yield. This result is similar to works with pure cultures of extremophile microorganisms where H-2 yields of 83% of the maximum were reported. We found higher concentrations of acetic acid in the digestates of thermophilic A-SSAD, while butyrate was in higher proportion in mesophilic A-SSAD spent solids. The moderate-to-high yields obtained with the semicontinuous process used in this work are in disagreement with previous reports claiming that batch and semicontinuous processes are less efficient than continuous ones. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.