Glycogen was isolated from Methanolobus tindarius and 4 species of Methanococcus. It was identified by the iodine reaction, determination of glucose, maltose and isomaltose in acid hydrolysates and partial acid hydrolysates, respectively, determination of erythritol and glycerol after periodate oxidation and treatment with amyloglucosidase. Glycogen particles in the cells are distributed throughout the cytoplasm. Ml. tindarius can use elemental nitrogen and cysteine as nitrogen source. The glycogen and polyphosphate content of cells of Ml. tindarius increased under nitrogen limitation. During incubation without external energy source, glycogen decreased and methane formation was correlated to the glycogen content of the cells.