BACKGROUND To evaluate the effect of the sustained-release formulation of indapamide (indapamide SR) in type 2 diabetic patients with mild-to-moderate hypertension and its possible side effects, particularly on glucose metabolism and lipid profiles. METHODS A total of 64 patients randomly received 1.5 mg of indapamide SR or placebo once daily for 3 months. The effects were evaluated by 24-h ambulatory blood pressure monitor, fasting blood sampling for biochemistry, lipid profiles, and frequently sampled intravenous glucose tolerance test. RESULTS The changes in standing and supine blood pressure (BP) were significant (154.7 +/- 9.4/94 +/- 2.9 mm Hg v 134.4 +/- 5.1/82.4 +/- 5 mm Hg and 155 +/- 9.8/94.6 +/- 3.6 mm Hg v 135.1 +/- 4.9/82.1 +/- 4.7 mm Hg) in the indapamide group, but not in the placebo group. According to the 24-h ambulatory blood pressure monitor reading, a significant reduction was observed in not only in the whole-day mean BP (mean systolic BP/mean diastolic BP, 149 +/- 19.3/87.6 +/- 11.3 mm Hg v 135.7 +/- 12.6/79.6 +/- 9 mm Hg) but also the whole-day mean median arterial pressure (109 +/- 12.7 mm Hg v 98.7 +/- 8.2 mm Hg) for the indapamide group, but not the placebo group. There were no changes in biochemical data including serum sodium, potassium, chloride, uric acid, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, creatinine, lipid profiles, fasting blood glucose, insulin, hemoglobin Alc, and glucose metabolism parameters (insulin sensitivity, glucose effectiveness, and acute insulin response) from frequently sampled intravenous glucose tolerance test after indapamide or placebo therapy. CONCLUSIONS Indapamide SR can significantly lower the whole-day BP in hypertensive patients with type 2 diabetes. Also, it did not alter or aggravate patients' lipid profiles, glucose metabolism, and did not exert possible side effects of hypokalemia and hyperuricemia. Therefore, monotherapy with indapamide SR should be suggested in type 2 diabetic patients with mild-to-moderate hypertension.