1. The effects of prazosin administered alone or in combination were studied in thirty patients between August 1974 and March 1975. 2. All patients had previously received treatment for hypertension with other agents, for from 2 months to 10 years. All thirty patients had refractory hypertension which had not responded satisfactorily to other treatment. 3. Patients were treated initially with prazosin; polythiazide, or polythiazide plus tolamolol, were added when necessary. 4. A satisfactory blood pressure response to prazosin alone, or prazosin in dual or triple combination therapy, occurred in all thirty patients. 5. Prazosin was well tolerated.