Fermentations of market garbage and water hyacinth in laboratory-scale solid-phase fermenters operated in fed batch mode is reported. Solid-phase fermentation was effected by a daily sprinkling of a weekly-fed biomass bed with an aqueous suspension of biodegradative bacteria to initiate and sustain high levels of biogas production. Gas production rates greater than 0.5 litres/litre per day at specific gas yields of 250-300 litres/kg total solids at residence times between 150 and 250 days were obtained. Major methanogenic activity appeared to occur in the lower parts of the decomposing bed, therefore feeding could be carried out on a once-weekly basis by opening the top of the fermenter and adding the untreated biomass feed, without deleterious effects on the overall gas yields or composition. The compaction of biomass feeds during decomposition permitted the use of high residence times without loss of space economy.