A restriction endonuclease fragment of the maxicircle of Trypanosoma brucei brucei kinetoplast DNA hybridizes with a cloned mitochondrial DNA sequence which encodes cytochrome oxidase subunit II of Zea mays. A cloned mitochondrial DNA sequence encoding cytochrome oxidase subunit II of Saccharomyces cerevisiae also hybridized with kDNA, but exhibits less homology with the maxicircle than does the maize gene. The hybridizing maxicircle DNA was localized to a 2.8 kbp segment which is bounded by TaqI restriction endonuclease sites and nearby HindIII and EcoRI restriction sites. The TaqI restriction fragment is conserved between T. brucei brucei, T. brucei rhodesiense and T. brucei gambiense and hybridizes with the Zea mays probe in each case.