Biomethanation of organic matter is now recognized as a viable alternative for production of energy. Among various biomass sources screened, Leucaena leucocephala, having a high biomethanation rate, has been identified as a potential substrate for large-scale methane generation. During semi-continuous fermentations at 30 °C with volatile solids (VS) ranging from 1.0-2.5 g l-1 at hydraulic retention time (HRT) ranging from 10-18 days, the yield of product gas per gram of volatile solids input was about 0.45-0.601 in the case of L leucocephala and 0.15-0.201 from cow-manure. Mass spectrometric analysis of the product gas from L leucocephala indicated a methane content of 78-80%. Batch fermentation for 80 days with input volatile solids of 40-44 g in a 21 digester resulted in a gas yield of 0.87 l g-1 volatile solids input for L leucocephala and 0.33 l g for cow-manure. The complex degradation of solid organic matter involves multiphase interactions between microbes and their environment; optimisation and separation of predominantly acidogenic and methanogenic species was achieved in a multi-stage digester with separate compartments. This design was used for degradation studies of L. leucocephala, which, from the results presented, appears to be a good candidate for an 'energy-farm' for large-scale biomethanation. © 1986.