The hyperglycemic responses to trichlormethiazide (4 or 8 mg daily) and chlorthalidone (50 or 100 mg daily) for eight weeks were evaluated in 27 hypertensive patients. Twelve patients were diabetic, seven prediabetic, and eight nondiabetic. There was a significant increase in the two-hour blood sugar after an oral glucose load in all three groups. The fasting blood sugar increased significantly by the first week of treatment in the diabetics and by the last week of treatment in the prediabetics, but there was no significant change in the nondiabetics. Alterations of the fasting and two-hour blood sugar were not dependent on drug or dose. Serum potassium, sodium, amylase, and uric acid were measured and showed no correlation with the changes in the two-hour blood sugar. Permanent diabetes was not induced in any of the nondiabetic or prediabetic patients.