A new genus, Methyluvorus, and one new species are described for a group of restricted facultatively methylotrophic bacteria. Five strains belonging to the new genus are characterized by a low level (5 to 15%) of DNA-DNA homology with type strains of restricted facultative methylobacteria of the genus Methyluphilus (M. methylutruphus NCIB 105 lST) and obligate methylobacteria of the genus Methylobacillus (M. glycugenes ATCC 2947ST). The Methyluvurus strains, like Methyluphilus and Methylobacillus strains, assimilate methanol via the ribulose monophosphate pathway and do not have a-ketoglutarate dehydrogenase and glyoxylate bypass enzymes. Methyluvurus strains are characterized by an enhanced specificity of 6-phosphogluconate dehydrogenase to NAD (not NADP) the absence of glutamate dehydrogenase, and the presence of the glutamate cycle enzymes for ammonia assimilation. The deoxyribonucleic acid base composition of the Methyluvurus strains is 56 to 57 mol% guanine plus cytosine. Their phospholipids are similar to those of Methylobacillus but differ from those of Methylophilus by the occurrence of diphosphatidylglycerol. The fatty acid composition of the strains of all three genera is primarily C16:lw7 and C16:o, although the Methyluphilus, but not Methyluvurus, strains also contain two unidentified C,, branched fatty acids. The type species is Methyluvorus glucusutruphus sp. nov. The type strain is 6B1 (= UCM B-1475). To date, three genera have been described for the obligate and restricted facultatively methylotrophic bacteria (methy- lobacteria) with the ribulose monophosphate (RUMP) path- way of C, assimilation. Marine methylobacteria were re- ferred to the genus Methylophaga (6, 18). All terrestrial strains of methylobacteria were divided into two genera, Methylobacillus and Methylophilus. The genus Methyloba- cillus was initially proposed for the nonmotile obligate methylobacteria (21). Later it was emended to be used for both obligate and restricted facultative methylobacteria (17). However, Jenkins et al. (8, 9) proposed to transfer the restricted facultative strains to a new genus, Methylophilus. The genus Methylobacillus should now be used only for the obligate methylobacteria. Although most of the known strains of obligate and restricted facultative methylobacteria can be placed in any of the above validated taxa, they still show a significant heter- ogeneity with respect to DNA-DNA homology and some phenotypic characteristics (7,9,19). Very recently, we have briefly described several strains of the restricted facultative methylobacteria having an intermediate taxonomic position between the genera Methylophilus and Methylobacillus. A new genus, Methylovorus, has been proposed for these strains (5). This paper presents the comparative characteri- zation and formal description of the new taxon.