A patient with clinically manifest hereditary hemochromatosis was found to be heterozygous for the c.845 A-->G (C282Y) mutation. As simple heterozygotes for this mutation do not develop the hemochromatosis phenotype, the coding region of the patient's HFE gene was sequenced and a previously undescribed nonsense mutation was identified at c.211 C-->T (R74X). The patient's brother who also had the hemochromatosis phenotype shared his HFE genotype. To determine how common such mutations might be, the coding and 5' region of the HFE genes of 11 subjects who had been found in a large population survey to be heterozygous for the C282Y mutation and had elevated ferritin levels were sequenced. No mutations were found. Sequencing of the HFE gene also revealed two polymorphisms that had not previously been noted, -467 C-->G and -970 T-->G. Neither of these mutations appear to cause an abnormality in iron metabolism.