The relationship between an improvement of the carbohydrate metabolism due to a four-week intensified conventional insulin treatment and changes in fatty acid patterns of serum lipids was investigated in 12 insulin-dependent diabetic patients. At the commencement of the study the diabetic patients were characterized by higher relative linolic acid contents in the serum cholesterolesters and phospholipids in comparison with control subjects. The intensified insulin treatment was associated with a significant improvement of the glycaemic control, whereas the fatty acid patterns of the serum lipids remained unchanged. The results demonstrate that short-time improvement of the carbohydrate metabolism is not associated with qualitative changes of serum lipids in insulin-dependent diabetic patients. Remains to be established the long-term effect of improved metabolic control on fatty acid metabolism.