SUMMARYA cDNA clone complementary to the mRNA encoding the human muscle specific carbonic anhydrase CA III has been used as probe in the analysis of DNA from panels of rodent/human somatic cell hybrids. The presence of the CA III gene in all hybrids correlates with the presence of chromosome 8. This is the first assignment of the CA III gene in any species and, together with published mapping data, indicates that all of the human CA loci are situated on chromosome 8.