Two anaerobic acidogenic reactors, one mesophilic (37 degreesC) and one thermophilic (55 degreesC), were operated with a synthetic wastewater at a series of organic loading rates (OLRs). There was almost no difference between the two reactors for chemical oxygen demand (COD) reduction, and degree of acidification at any given OLRs. However, the thermophilic reactor had a higher substrate degradation rate, biogas production rate, and specific formation rate of aqueous products than the mesophilic reactor. The predominant acidogenic products in the two reactors were acetate, propionate, butyrate, and ethanol. The distribution of acidogenic aqueous products was significantly influenced by OLR, but not by temperature. Only 1.7-7.9% of the COD in wastewater was converted to hydrogen/methane for the mesophilic reactor, and 2.5-8.8% of the COD for the thermophilic reactor. (C) 2002 Elsevier Science Ltd. All rights reserved.