Methane-producing microorganisms (methanogens) catalyze the terminal reactions in the anaerobic digestion of biomass. This is a well-established biotechnological process used for both waste treatment and the production of the renewal energy source methane. Although methanogens are procaryotes they are not closely related to well-known eubacterial species, commonly termed bacteria, but are members of the third biological kingdom, the Archaebacteria. The paper presents a brief review of the information currently available documenting the structure of genes in methanogens. A comparison of gene structure in eubacteria, eucaryotes and methanogens is given. Evidence is presented indicating that polypeptide-encoding genes in methanogens are organized into operons and that translation is coordinated, as in eubacteria, by messenger ribonucleic acid:16S ribosomal ribonucleic acid hybridization. Methanogen-derived genes are expressed when cloned in Escherichia coli, which should allow routine genetic engineering procedures to be used to dissect and manipulate the bioprocess of methanogenesis.