The alpha subunit of the F(1)-ATPase complex of maize is a mitochondrial translational product, presumably encoded by the mitochondrial genome. Based on nucleotide and amino acid homology, we have identified a mitochondrial gene, designated atpalpha, that appears to code for the F(1)-ATPase alpha subunit of Zea mays. The atpalpha gene is present as a single copy in the maize. Texas cytoplasm and is actively transcribed. The maize alpha polypeptide has a predicted length of 508 amino acids and a molecular mass of 55,187 daltons. Amino acid homologies between the maize mitochondrial alpha subunit and the tobacco chloroplast CF(1) and Escherichia coli alpha subunits are 54 and 51%, respectively. The origin of the atpalpha gene is discussed.