An open study was carried out in general practice to assess the effectiveness and tolerance of labetalol in the treatment of 53 difficult hypertensive patients, most of whom had failed to respond to previous hypotensive therapy. The results showed that in the 49 patients receiving treatment for more than 3 months good blood pressure control was readily achieved, and with labetalol alone in all but 6 of them. The majority were controlled on doses ranging from 300 to 600 mg per day. Treatment was discontinued in 3 patients because of severe side-effects. Mild, tolerable side-effects, similar to those found with beta-adrenergic blocking agents, were reported by 35 patients.