The aim of the work described here was to analyse the biomethanization process for three types of organic fraction of municipal solid waste (OFMSW) using two different inoculum sources in a sequential leach-bed anaerobic reactor under thermophilic (55 degrees C) and dry conditions (20%TS). The OFMSWs studied were: separately collected food waste (SC_OFMSW) from restaurants, synthetic waste (ST_OFMSW) and mechanically selected municipal waste (MS_OFMSW). The inoculum studied were digested mesophilic sludge (SLUDGE) and digested SC_OFMSW. The results show that SLUDGE gave the best performance and this was therefore selected for the rest of the experiments. Three assays were performed to analyse the biomethanization processes of three types of organic waste. The results suggest that all three wastes give rise to an acclimation stage with acidogenic/acetogenic activity between days 5 and 20-30 and a stabilization phase associated with methanogenic activity. In conclusion, a mixture of OFMSW (regardless of its origin) and SWINE arranged in layers in the reactor, as well as SLUDGE used with an inoculum source, enhanced the fast start up phase of a modified sequential leach-bed system under dry thermophilic conditions. (c) 2006 Elsevier Ltd. All rights reserved.