Serum ceruloplasmin values of less than 21.0 mg/100 ml in males or less than 23.0 mg/100 ml in females were observed in 14 out of 156 otherwise healthy members of a pedigree. The hypoceruloplasminemia segregated in a fashion suggesting that the affected individuals are heterozygous for a mutant gene that results in hypoceruloplasminemia. This mutant gene could be a Wilson's disease gene, but excessive copper loading was absent. It is suggested that hereditary hypoceruloplasminemia may be a benign entity distinct from Wilson's disease.