PARTIAL ileal bypass surgery was performed in 3 patients with heterozygous familial hypercholesterolemia who had previously received conventional therapy. During the ensuing 3 years there was a moderate and sustained reduction in serum total cholesterol (27%). There was no significant alteration in HDL cholesterol. The operation was well tolerated with minimal morbidity. There were no serious haematological, hepatic cr nutritional side-effects and bacterial contamination of the upper jejunum was minimal. Despite the reduction of circulating cholesterol there was progression of coronary artery disease.