In the specialized clinic for disorders of the lipid metabolism 27 patients, 8 men and 19 women, heterozygotes with familial hypercholesterolaemia were treated for 8 weeks with Colestid (colestipol bags a 5 g, Upjohn, Belgium). The administered dose was 15 g colestipol per day. After colestipol treatment the authors recorded a statistically significant decline of total cholesterol by 18% and of LDL-cholesterol by as much as 27%. The apolipoprotein B concentration declined during treatment by 9% and concurrently there was a favourable rise of apolipoprotein A-1 by 20%. The authors recorded also a slight rise of the HDL-cholesterol concentration which, however, was not statistically significant. The serum triglyceride level increased slightly after colestipol treatment. It did not prove possible to influence the lipoprotein(a) level by colestipol administration. As compared with other hypolipidaemic agents from the group of ion exchange resins, the patients tolerated Colestid surprisingly well. Only one female patient discontinued treatment because of dyspeptic complaints, severe constipation.