Abstract
Nine strains of Pseudomonas maltophilia which do not require methionine are described. Methionine-requiring and -nonrequiring strains of P. maltophilia belong to different biovars, which are designated I and II, respectively; they differ from each other with respect to phenotypic characteristics, cellular fatty acid composition, deoxyribonucleic acid base composition, and deoxyribonucleic acid-deoxyribonucleic acid hybridization. The relationship of P. maltophilia to Xan-thomonas species is also discussed.