Peroxide haemolysis of erythrocytes in children with diabetes mellitus was discussed. The peroxide haemolysis tests of erythrocytes of 32 healthy and 35 diabetic children were compared. The erythrocytes of diabetics were hemolyzed to a small extent when 2% H2O2 was used. If 5 and 10 mmol/l glucose were added, the peroxide haemolysis of the controls decreased but that of the diabetics did not change. The results of the examinations performed with pH 6.8 were compared to those of pH 7.4 and both in the diabetics and controls a slight haemolysis was observed.