Methanosarcina barkeri strains (227, MS, and UBS) were tested for their ability to utilize pyruvate for growth and methanogenesis. All three strains grown on methanol required 4-5 weeks of adaptation for growth on pyruvate, whereas they required only 2-3 weeks of adaptation for growth on acetate. The adapted cells had a lag of 3-4 days for growth on acetate and 5-10 days for growth on pyruvate. Equimolar amounts of methane were produced from acetate, whereas 0.6-0.7 mol of methane was produced per mol of pyruvate. The optimal concentration of pyruvate for growth and methanogenesis for all three strains was 100 mm, and doubling times were in the range of 135-170 h.