Methanogenesis is a major pathway in the global cycling of carbon. Anaerobic biodegradation is used both for detoxification and disposal of wastes and for conversion of biomass to the readily combustible fuel, methane. The microorganisms that synthesize methane, the methanogens, are anaerobic archaebacteria; however, methanogen genes have been shown to closely resemble eubacterial genes and that they can be functionally expressed in eubacterial cells. The possibility therefore exists to use recombinant DNA procedures to investigate and dissect the regulation and biochemistry of methanogenesis. The paper analyzes currently available biochemical information to identify enzymes essential for methanogenesis, enzymes that could therefore be considered to be encoded by methane genes. (Copyright (c) 1988 John Wiley & Sons Ltd.)