Reconstituted municipal solid waste (MSW) with varying contents of putrescible and cellulosic waste was incubated anaerobically under mesophilic conditions. Standard physicochemical parameters were monitored, together with stable isotopic signatures of produced CH4 and CO2. δ13C values for CH4 indicated a change of methanogenic metabolism with time. CH4 was predominantly produced from H2/CO2 at the beginning of the incubations. This period was associated with important shifts in archaeal communities monitored by automated ribosomal intergenic spacer analysis (ARISA) and FISH of oligonucleotidic probes targeting specifically 16S rRNA gene of various methanogenic groups. The onset of the active methane generation phase was characterized by an increase of CH4δ13C, indicating a progressive shift toward an aceticlastic metabolism. When the methane production levelled off, a decrease in the isotopic signature was observed toward values characteristics of hydrogenotrophic metabolism. ARISA profiles were, however, found to be stable from the beginning of the active methane generation phase until the end of the experiment. FISH observation indicated that members of the family Methanosarcinaceae were predominant in the archaeal community during this period, suggesting that these methanogens might exhibit a high metabolic versatility during methanization of waste.