The authors investigated selected indicators of the lipid metabolism in 31 children with insulin-dependent diabetes for a period of 3 to 14 years. They divided the patients into two groups those with a glycosylated haemoglobin below or above 9 mumol/1 g haemoglobin. They compared the assembled results of the two groups and also with the results obtained in a control group. The total cholesterol was in both diabetic groups higher than in healthy subjects and was higher than the value which is considered from the aspect of the genesis and development of atherosclerosis as a risk value. Children with poorly compensated diabetes, i. e. with a glycosylated Hb level above 9 mumol had a higher cholesterol level as compared with well compensated diabetic children. The pre-beta fraction of lipoprotein increased in both groups of patients, however, more in those where the disease was not well compensated. There was a parallel decrease of the alpha fraction and the lipoprotein profile had a markedly atherogenic character. The apolipoprotein B concentration was in patients with well compensated diabetes lower, as compared with controls but in patients with poorly compensated diabetes after 4-5 years treatment is was significantly higher. Poor compensation of diabetes led after 4-5 years duration to a significant rise of the serum triglyceride level. As the blood lipid levels are influenced in a significantly way by diet, compensation of the disease and a low-fat diet are essential with regard to the results assembled in this investigation for prevention of ischaemic heart disease in diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)