The effects of oxprenolol and propranolol on the venoconstrictor response to noradrenaline were studied in healthy volunteers by measuring superficial dorsal hand vein diameter at a standard congesting pressure. In 8 subjects dose response curves to noradrenaline (20-1280 ng/ml) were obtained with noradrenaline alone, with noradrenaline plus propranolol 10 microgram/ml, with noradrenaline plus propranolol 10 microgram/ml plus oxprenolol 3 microgram/ml and with noradrenaline plus propranolol 13 microgram/ml according to a double blind balanced randomised design. Propranolol 10 microgram/ml significantly (p less than 0.05) potentiated the vasoconstrictor response to noradrenaline and the addition of oxprenolol significantly (P less than 0.05) reversed the potentiation giving a response similar to that seen with noradrenaline alone. The higher concentration of propranolol did not produce further potentiation, the response being similar to that obtained with the lower concentration of propranolol. It is suggested that the effect of oxprenolol may be attributable to alpha blocking properties, to partial beta agonism or to its membrane stabilising properties.