The anti-hypertensive efficacy of combined alpha- and beta-adrenoreceptor blockade with phentolamine-oxprenolol or with labetalol (AH 5158).

1. The interaction of phentolamine with the beta-receptor blocker oxprenolol was studied in a controlled trial. 2. The combination was generally well tolerated. 3. Oxprenolol alone produced modest but significant reductions in supine, standing and post-exercise blood pressures. Small reductions were seen only with sustained phentolamine administration. 4. The combined effect of the two drugs appeared to be additive only at the lower doses of oxprenolol. 5. Labetalol produced significantly greater reductions in supine and standing blood pressure than combined oxprenolol-phentolamine. At a daily dose of 400 mg, postural hypotension was not seen, though transient symptoms were frequent.