After two weeks' treatment of indapamide (2.5 mg/d) in 30 cases of mild to moderate hypertensive patients, there was a significant decline of systolic and diastolic blood pressure. And 8 weeks after indapamide administration, 2/3 of the total treated patients achieved complete control of hypertension. During the treatment period, there were no changes of serum cholesterol, triglyceride and renal function, except a slight, but still in the normal range, decrease of serum potassium and sodium. Concurrently, plasma vasoconstrictive prostaglandins TXB2 (metabolite of TXA2) and PGF2 alpha reduced significantly (P < 0.01 and P < 0.001 respectively), whereas plasma vasodilative prostaglandins 6-keto-PGF1 alpha (metabolite of PGI2) and PGE2 increased significantly (P < 0.02 and P < 0.05 respectively). The results support the theory that prostaglandins system may play an important role in the hypotensive process of indapamide. The influence of indapamide on prostaglandin system may favour the improvement of platelet function and the maintenance of the homeostasis.