Cell envelopes from logarithmic phase cells of eight strains ofAgrobacterium tumefacienswere isolated and examined qualitatively and quantitatively for various components. Envelopes, 6 to 9% of the total dry weight of the bacteria, were composed of approximately 23 to 27% lipid, 3.1 to 6.0% total nitrogen, and 6.3 to 11.2% carbohydrates. Cytochrome was present in envelopes obtained from logarithmic phase cells.The glycosaminopeptide was composed of glutamic acid, alanine, 2,6-diaminopimelic acid, and amino sugars. Leucine, phenylalanine, serine, and aspartic acid were found in relatively high levels in several of the strains investigated.In addition to ubiquinones, four phospholipids, phosphatidylethanolamine, phosphatidyl-N-methylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidyl-choline, were observed in the lipid fraction of all eight strains ofA.tumefaciensexamined.Glucose, fucose, and 2-keto-3-deoxyoctulosonic acid were present in the lipopolysaccharide of all strains tested.There appears to be no correlation between the virulence of this plant pathogen and the mucopeptide or lipid–protein–polysaccharide components of the cell envelope.