A low dose (1.25 mg) of indapamide (Lozol, Rhône-Poulenc Rorer Pharmaceuticals, Collegeville, PA) was evaluated in 222 elderly patients (> or = 50 years) with mild to moderate essential hypertension in a multicenter, randomized, double-blind, parallel-group clinical trial. A 4-week single-blind placebo washout period was followed by an 8-week double-blind treatment period. Patients were randomized to receive indapamide 1.25 mg/day or to receive placebo. The primary efficacy variable was the mean change in sitting diastolic blood pressure from baseline to week 8. Eighty-one patients in the indapamide group (73%) and 87 patients in the placebo group (78%) completed the 8 weeks of double-blind therapy. Therapy with 1.25 mg of indapamide produced greater reductions compared with placebo in sitting diastolic blood pressure after 8 weeks of therapy, with statistical significance (P < or = 0.0015) seen after only 2 weeks of therapy and continuing throughout the 8 weeks. All secondary efficacy measures (sitting systolic blood pressure, standing systolic and diastolic blood pressures, and > or = 10 mm Hg decrease or final value of < or = 90 mm Hg in sitting diastolic blood pressure) also showed superior (P < or = 0.0014) improvement in the indapamide group compared with placebo after 8 weeks of double-blind treatment. During the 8-week double-blind treatment period, incidence rates for all adverse events and for drug-related adverse events were similar between the two treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)