A study is presented of a 48-year-old female patient and her three siblings with familial hypercholesterolemia. The family members had episodes of cerebral infarction and apparently had atherosclerosis of the internal carotid artery, but no coronary heart disease due to their almost normal level of cholesterol. The laboratory studies of the family members revealed the elevations of serum lipid peroxides, serum lipoprotein(a), leukotriene C 4 in blood, the thromboxane B 2 6- keto-prostaglandin F 1α ratio in plasma and serum hydroxyl radical. Therefore, it is suspected that these factors accelerating atherosclerotic process caused the cerebral infarction. The patient demonstrated corneal opacities, palpebral xanthomas, thickened Achilles tendons, polyneuropathy and the carpal tunnel syndrome. Laboratory studies revealed an elevation in the OKT4 8 ratio, monocyte dysfunction with respect to phagocytosis and chemotaxis, and the presence of the 46 XX 45 XO mosaic chromosome. Lipid deposits were observed in the Achilles tendon, the transverse carpal ligament, the Schwann's cells and axons of the sural nerve, and in the keratocytes and stroma of the cornea. Following the administration of tocopherol nicotinate and probucol, the patient's serum lipid peroxide normalized and there was improvement in her palpebral xanthomas, thickening of the Achilles tendons and polyneuropathy. We conclude that the lipid deposits in this patient were due to the abnormal oxidative metabolism of low-density lipoprotein and a disturbance of the scavenger pathway due to the monocyte dysfunction.