In humans, the H (heavy) and L (light) chains of the iron-storage protein ferritin, are derived from multigene families. We have examined the chromosomal distribution of these H and L sequences by Southern analysis of hybrid cell DNA and by chromosomal in situ hybridization. Our results show that human ferritin H genes and related sequences are found on at least seven different chromosomes while L genes and related sequences are on at least three different chromosomes. Further, we have mapped the chromosomal location of expressed genes for human H and L ferritin chains and have found an H sequence which may be a useful marker for idiopathic hemochromatosis.