Mitochondrial DNAs were prepared from maize lines with normal cytoplasm and with the T, C, S, and EP sources of male-sterile cytoplasms. Agarose gel electrophoresis of these preparations revealed a main high-molecular-weight DNA band. In addition, the S cytoplasm was characterized by the presence of two faster migrating DNAs of molecular weight 3.42 to 3.48 x 10(6) and 4.01 to 4.10 x 10(6). Electron microscopy showed these unique DNAs to be of different length, but their molecular configuration was not clearly established. It is possible that these unique DNAs represent physical evidence of an episomal system previously postulated to function in the S male-sterile cytoplasm.