Ferritin is the intracellular iron storage protein. Tissue ferritin stores are markedly increased in hemochromatosis, a disease of iron overload that has been linked to chromosome 6. In order to provide further information concerning the genetics of ferritin synthesis and to determine if the structural gene for ferritin was on chromosome 6, studies were performed to identify the human chromosome that contains the ferritin gene. Ferritin immunoassays were performed on extracts of Chinese hamster ovary somatic cells that were hybridized with human lymphocytes and fibroblasts and contained various human chromosomes in different combinations. None of the 13 cell lines that lacked immunoreactive human ferritin contained chromosome 19, and all 9 of the cell lines that produced human ferritin contained chromosome 19. No other human chromosome shared this association with human ferritin. In studies of subclones of ferritin-positive cell lines, immunoreactive ferritin consistently segregated only with chromosome 19. Immunoprecipitation studies performed on cells that had been incubated with 59Fe-containing transferrin indicated that chromosome 19-containing cells incorporated iron into intact and functional molecules of human ferritin. The necessary and exclusive association of chromosome 19 with human ferritin indicates that a defect in the structural gene for human ferritin cannot account for the abnormalities of hemochromatosis. Moreover, this hamster-human hybrid cell system should prove useful in further studies of regulation of ferritin concentration and composition.