1 The effects of oxprenolol and propranolol on peripheral blood flow were compared in patients with mild and moderate essential hypertension. 2 In an acute double-blind crossover study in which eight patients participated there was a significant reduction in resting forearm blood flow (RFBF) 2 h after 80 mg propranolol (mean +/- s.e. mean) (-0.87 +/- 0.13 microliter min-1 100 g-1) and after 80 mg oxprenolol (-0.30 +/- 0.12) but not after placebo. This reduction was significantly greater after propranolol (P = 0.022). 3 Seven patients continued into a double-blind crossover study comparing the above dose of the two drugs twice a day. On both the beta-adrenoceptor blockers there was a significant reduction in blood pressure after 2 weeks of treatment and also a significant reduction in RFBF. 4 After 6 weeks treatment with propranolol the reduction in RFBF persisted and was significantly less (P = 0.04) than after 6 weeks treatment of oxprenolol, at which time RFBF was back to control. 5 There were no consistent changes in skin temperature. 6 Neither propranolol nor oxprenolol should be used in patients with severe peripheral vascular disease. 7 If beta-adrenoceptor blockade is necessary in patients with mild peripheral vascular disease oxprenolol should be used in preference to propranolol but should be prescribed with caution.