Mitochondrial DNA was isolated from rice with normal (fertile) and male sterile cytoplasms were analyzed by electrophoresis, the patterns were readily distinguishable between the two cytoplasmic types. It was found that mitochondria from male sterile cytoplasm contain DNA species of sizes 1.5 kilobase pairs (kb) and 1.2kb, in addition to the DNA of relatively much higher molecular weight. In contrast mitochondria from normal cytoplasm contained only one of these DNA species, that of higher molecular weight.