A methanogen utilizing methanol was isolated from a reactor anaerobically degrading leaves of Leucaena leucocephala. The cells are rods of length 2.2 μm with diameter 0.46 μm also occurring in short chains. The cells stain gram-positive and the G+C content is 52.8 mol%. Growth occurred optimally with methanol (0.1 M) at 37°C and pH 7.4 with a doubling time of 7.5 h. The preferred sulfur source was glutathione. In addition to methanol, the isolate utilized 2-propanol as carbon and hydrogen source and also grew effectively on H2+CO2. Electron microscopy revealed the cell enveloped in triple layers consisting of a cell membrane and a cell wall separated by an electron transparent space with the nuclear zone at the centre of the cytoplasm. Presence of cytochromes was evident in the membrane fractions. The isolate possesses novel features. © 1991 Springer-Verlag.