Hypoinsulinemia in type 1 diabetes may theoretically inhibit fatty acid desaturases and, consequently, the conversion of essential fatty acids to long-chain polyunsaturated fatty acids (LCPUFA).Previously we reported significantly higher plasma values of the essential fatty acids, but significantly lower values of LCPUFA in diabetic children than in healthy controls.We also determined fatty acid composition of plasma and erythrocyte membrane lipids in young diabetic adults and in age-matched healthy controls and found that alues of linoleic acid and arachidonic acid (C20:4n-6, AA) were significantly higher, whereas docosahexaenoic acid (C22:6n-3, DHA) values were significantly lower in diabetic than in control subjects.These data suggested that the availability of n-3 LCPUFA may be reduced in diabetes.On this basis we investigated the acute effect of diabetic ketoacidosis (DKA) on the fatty acid composition of plasma lipids.Diabetic children (n=9;age: 16.1 [3.3] y;duration of diabetes: 5.0 [5.3.] y;daily insulin dose: 0.87 [0.66] unit/kg body weight/d;glycated haemoglobin:13.4 [2.8] %;median [IQR]) were investigated during and after DKA.Blood glucose and other conventional laboratory parameters were grossly abnormal during but net after DKA.Values of the n-6 essential fatty acid, linoleic acid (C18:2n-6) were significantly lower after than during DKA, whereas values of AA were significantly lower during than after DKA.Also the product/substrate ratios for delta-6 desaturation were significantly lower during than after DKA.This observation suggests that disturbances of essential fatty acid metabolism in diabetic children are related not only to diet but to hypoinsulinaemia as well.We also investigated changes of fatty acids in plasma phospholipids in a diabetic teenager during and after nine subsequent episodes of DKA.Plasma phospholipid linoleic acid values significantly decreased, while values of dihomo-gammalinolenic acid (C20:3n-6) and docosatetraenoic acid (C22:4n-6) significantly increased.Values of alpha-linolenic acid (C18:3n-3) did not change, while values of DHA were significantly higher after than during DKA.These data obtained in the same patient during repeated episodes of DKA support the concept that hypoinsulinemia plays an important role in disturbances of essential fatty acid metabolism in diabetes.In summary, successful treatment of DKA is associated with a significant increase of LCPUFA values in blood plasma in diabetic children.In conclusion, disturbances of essential fatty acid metabolism in diabetic children may be related not only to dietary factors, but to subnormal availability of insulin as well.