Diabetes mellitus is associated with disturbances in electrolyte metabolism. We studied 68 patients with insulin-requiring diabetes mellitus followed up in the Home Monitoring Clinic in order to assess the relationship between electrolyte disturbances and severity of diabetes. There is a significant correlation of serum sodium (r = -0.323, P less than 0.01), potassium (r = 0.416, P less than 0.001), magnesium (r = -0.292, P less than 0.02) with fasting glucose. Thus, in patients with high fasting blood glucose, sodium and magnesium tend to be lower while potassium is higher. Among the three parameters, only serum magnesium significantly correlates with the level of hemoglobin A1 (r = -0.356, P less than 0.001) and thus may be related to the long-term control of diabetes. On the other hand, the hyponatremia and hyperkalemia are more likely to be related to short-term metabolic control as reflected by fasting blood glucose. To conclude, minor changes in electrolytes have been found in a group of 68 Chinese patients receiving insulin. There is a remote possibility that these electrolyte changes may influence the chemical events responsible for long-term diabetic complications.