Excessive absorption of dietary iron results in pathologic hepatic iron accumulation in the genetic disorder hemochromatosis. Genetic factors have also been suggested to play a role in African iron overload that is induced by the intake of iron-rich fermented beer. We have used inbred strains of mice to investigate previously unrecognized genetic factors controlling iron metabolism. Among different strains of mice fed a basal iron diet, serum iron levels varied twofold. In contrast, serum transferrin levels were remarkably constant. This indicates that transferrin saturation with iron, but not the serum level of transferrin, is likely to be genetically determined in mice. Hepatic iron stores also varied twofold among the different mouse strains. Remarkably, hepatic iron stores failed to reflect transferrin saturation, suggesting that different genetic factors control transferrin saturation and hepatic iron stores. When mice were challenged with a high-iron diet, the concentration of carbonyl iron required to completely saturate transferrin with iron was 10 times greater for C57BL/6 and BALB/c mice than for DBA/2 and AKR mice. These results are reminiscent of the iron-loading locus proposed to interact with dietary iron in African iron overload. Our studies with inbred strains of mice have revealed a number of novel control points in iron metabolism that may be genetically determined. The mouse model may thus be useful for understanding the molecular basis of hemochromatosis and African iron overload.