A 14-yr-old Turkish girl presented with serum cholesterol levels of 15-20 mmol/l, skin and tendon xanthomata, and anginal attacks. A coronary angiography demonstrated severe coronary atherosclerosis including a 70% stenosis at the origin of the left coronary artery. The clinical diagnosis, homozygous familial hypercholesterolaemia, was confirmed by: (1) investigation of the family revealing hypercholesterolaemia in both her parents and siblings; (2) fibroblast association studies, in which the specific association of low density lipoprotein (LDL) was 35% of normal; and (3) LDL turnover study, in which the fractional catabolic rate of LDL was decreased to 0.213 pools/day. Treatment with cholestyramine or simvastatin had little effect on serum cholesterol levels. After coronary artery bypass grafting, the patient was treated with selective LDL apheresis using columns containing dextran-sulphate bound to cellulose. These columns bind apolipoprotein B containing lipoproteins but not high density lipoproteins. After 2 yr of therapy, the level of serum cholesterol has declined by 56%. Skin xanthomata have disappeared and there is no recurrence of angina pectoris. On repeated coronary angiography, two of the three bypasses are patent and there is no progression of atherosclerotic lesions. We conclude that LDL apheresis is an efficient procedure to lower serum cholesterol in patients who do not respond to pharmacological treatment of hypercholesterolaemia.