Heredopathia atactica polyneuritiformis (phytanic-acid storage disease, Refsum's disease) is an inborn error of metabolism, in which the body accumulates exogenous phytanic acid. The severe manifestations of this disease, which include pigmentary retinal degeneration, chronic polyneuropathy, ataxia, impaired hearing, and cardiopathy, can be either kept from worsening or reversed by elimination of foods rich in phytanic acid from patients' diets. This is borne out by a 20-year experience with two patients, whose conditions improved markedly once they stopped eating butter, animal fat, and other foods rich in phytanic acid.