Desulfovibrio desulfuricans and Acidianus brierleyi were used to study hydrogenation of coal, pretreated coal, asphaltenes, and model compounds [diphenyl methane (DPM) and fumarate] under anaerobic conditions. This study involved three primary aspects : (1) determination of net hydrogen-uptake, (2) identification of the biohydrogenated product of fumarate, and (3) testing the influence of hydrogen uptake/biohydrogenation of coal in terms of direct liquefaction yield. The net hydrogen uptake values (from Warburg and GC assays) by the coals or the model compounds (controls) were less than that of the biotreated samples. The greatest hydrogen uptake (net, 1878 mumol g-1; coal control, 245; cell control, 127) occurred in untreated coal KCER No. 4677 in the presence of D. desulfuricans. The net hydrogen uptake by coals varied depending upon the coal type and the microorganism. Model compound DPM showed its highest hydrogen uptake rate when catalysed by D. desulfuricans (150 mumol g-1 h-1). D. desulfuricans also hydrogenated 36% of the fumarate to succinate in the presence of hydrogen. Biotreated coal KCER No. 4677 (with 1878 mumol H-2 g-1) was subsequently subjected to direct liquefaction. It showed a net increase in liquefaction yield of 5-4% as a result of the biotreament.