A placebo-controlled trial was carried out in 20 hypertensive patients to evaluate the therapeutic efficacy of 2.5 mg indapamide per day. Hypertension had been present for at least 2 years in all patients and they had previously been treated with a variety of other antihypertensive drugs. These were withdrawn on entry to the trial and patients received 1 tablet of placebo per day for 15 days before being treated with 1 tablet (2.5 mg) indapamide per day for 1 month. The results showed a statistically significant decrease in systolic, diastolic, and mean arterial blood pressures compared with after placebo, with a level of antihypertensive effect similar to that of the previous treatment. In 8 patients who did not show a satisfactory response, treatment was continued for a further month on 5 mg indapamide per day. A reduction in blood pressure levels occurred and was associated at this higher dosage with a significantly increased urine output. Subjective symptoms such as headache, dizziness and tinnitus responded satisfactorily to treatment, and side-effects were absent, apart from transient weakness reported by 1 patient on the 5 mg regimen. Blood sugar levels remained unchanged in all patients, including the 4 diabetics who were treated, and no significant changes were noted in any of the other clinical or biochemical parameters investigated.