Tight linkage between the hemochromatosis locus and the HLA region permits determination of genotype in members of hemochromatosis pedigrees. To determine if simple laboratory measures of iron metabolism could predict the affected genotype without the need for HLA typing, we studied seven measures of iron metabolism: serum iron concentration, total iron-binding capacity, per cent saturation of transferrin, serum ferritin concentration, deferoxamine-induced urinary iron excretion and hepatic iron concentration evaluated by both chemical and histological methods. Discriminant analysis showed a per cent saturation of transferrin above 62% to be the best simply-measured indicator of the affected genotype: homozygosity is accurately predicted in 92% of the cases. The logarithmic transform of serum ferritin concentration was only 71% accurate. Pedigree analysis estimated the frequency of the hemochromatosis gene at 0.069 +/- 0.020 with a recombination probability of 0.015 +/- 0.015 with the HLA region. This corresponds to a heterozygote frequency of 0.13 and a disease frequency of 0.005.