Indapamide (Lozol), an indoline antihypertensive drug with diuretic and vasodilating activities, was evaluated in 195 patients with mild to moderate essential hypertension (sitting DBP between 95 and 110 mmHg) in a multicentre, randomised, double-blind, parallel-group design trial. A four week single-blind placebo wash-out period was followed by an eight week double-blind period. Patients were randomised to indapamide 1.25 mg/day or to placebo. The primary efficacy endpoint was the mean change in sitting DBP from baseline to week 8. Ninety patients in the placebo group (93%) and 82 patients (84%) in the indapamide group completed the eight weeks of double-blind therapy. Indapamide produced a mean (SE) decrease in sitting DBP of 7.4 (0.63) mmHg (from 100.1 to 92.8 mmHg) compared with it decrease of 3.6 (0.75) mmHg (from 99.6 to 95.8 mmHg) produced by placebo (p < 0.0001). Indapamide and placebo also produced mean decreases in standing DBP of 6.8 (0.75) and 2.8 (0.77) mmHg, respectively (p = 0.0002), in sitting SBP of 11.1 (1.18) and 3.2 (1.35) mmHg, respectively (p = 0.0001) and in standing SBP of 11.4 (1.29) and 4.0 (1.43) mmHg, respectively (P = 0.0002). Reduction in BP of greater than or equal to 10 mmHg or to a DBP of less than or equal to 90 mmHg was more frequent (P = 0.0005) among indapamide (46.6%) compared with placebo (23.7%) treated patients. During the eight week double-blind treatment period, incidence rates for all adverse experiences and for drug-related adverse experiences were similar between the two treatment groups. Three patients in the indapamide group and two patients in the placebo group were discontinued due to adverse events. Of 15 patients in the indapamide group who had normal potassium values at baseline and abnormally low Values during treatment, only four continued to have low potassium levels at week 8. Three of these patients received potassium supplements concomitant with double-blind medication. There were no clinically meaningful change in cholesterol or glucose in the indapamide group. In summary, indapamide given in a low dose proved to be safe and highly effective in the treatment of mild to moderate hypertension.