A methanogenic archaeon, strain MK4T, was isolated from ancient permafrost after long-term selective anaerobic cultivation. The cells were rods, 2.0–8.0 μm long and 0.40–0.45 μm wide, and stained Gram-negative. Optimal growth was observed at 28 °C and pH 7.0–7.2 and in 0.05 M NaCl. The isolate used H2 plus CO2, methylamine plus H2 and methanol plus H2 as sources for growth and methanogenesis. Phylogenetic analysis of the 16S rRNA gene sequence of the strain showed close affinity with Methanobacterium bryantii (similarity >99 % to the type strain). On the basis of the level of DNA–DNA hybridization (62 %) between strain MK4T and Methanobacterium bryantii VKM B-1629T and phenotypic and phylogenetic differences, strain MK4T was assigned to a novel species of the genus Methanobacterium, Methanobacterium veterum sp. nov., with the type strain MK4T (=DSM 19849T =VKM B-2440T).