The fatty acid compositions and multiple antibiotic resistance patterns of 32 strains of Bradyrhizobium japonicum correlated with two major deoxyribonucleic acid homology groups. In group I, the fatty acid composition was 1.3% 16:1 cis9 acid, 3.6% 16:1C acid, 8.8% 16:0 acid, 1.2% 19:0 cyclopropane acid, and 81.2% 18:1 acid. Group II contained 0.5% 16:1C acid, 11.1% 16:0 acid, 0.8% 17:0 cyclopropane acid, 24.7% 19:0 cyclopropane acid, and 62.3% 18:1 acid. Group I strains were susceptible to rifampin (500 μみゅーg/ml), tetracycline (100 μみゅーg/ml), streptomycin (100 μみゅー/ml), chloramphenicol (500 μみゅーg/ml), erythromycin (250 μみゅーg/ml), carbenicillin (500 μみゅーg/ml), and nalidixic acid (50 μみゅーg/ml), whereas group II strains were resistant to these antibiotics. Both groups were resistant to trimethoprim (50 μみゅーg/ml) and vancomycin (100 μみゅーg/ml).