p97 is a 97,000 molecular weight cell-surface glycoprotein, which is present in human melanomas but in only trace amounts in normal adult tissues. Amino acid sequence and iron binding studies have shown that p97 is structurally and functionally related to transferrin. Reports that the genes for the transferrin receptor (TR) and possibly transferrin are located on chromosome 3 prompted us to investigate the chromosomal localization of the p97 gene. Our strategy was to characterize interspecies somatic cell hybrids derived from human fibroblasts or lymphocytes for expression of p97 and presence of human chromosomes. Although fibroblasts and lymphocytes express only small amounts of p97, we were able to type the hybrids for p97 by using monoclonal antibodies in highly sensitive and specific immunoassays. Of 14 hybrids, 6 contained chromosome 3 and expressed p97, and 8 were negative for both. We conclude that the p97 gene, like the transferrin and TR genes, is located on chromosome 3.