1. Twenty patients with severe or moderate hypertension were treated with minoxidil for 284 patient-months. 2. The blood pressure was controlled in all patients, including those refractory to maximal doses of conventional anti-hypertensive agents. 3. In patients with moderate hypertension control with minoxidil was achieved earlier and more easily than with hydrallazine. 4. Three patients developed secondary resistance and required addition of guanethidine or increased doses of diuretics. 5. Fluid retention and hypertrichosis were the main side effects with minoxidil.