In two consecutive series of hypertensive patients the hypotensive effect, the hyporeninaemic effect and the blockade of cardiac beta-receptors was studied using weekly increasing doses of propranolol or atenolol. With both beta-blockers, cardiac blockade and hypotensive effect increased in a parallel fashion when the dosage was increased suggesting that the hypotensive effect is related to cardiac beta-blockade. On the other hand lack of parallelism between the hypotensive effect and the hyporeninaemic effect suggests that the hypotensive effect was not related to a major extent to the hyporeninaemic effect of the drugs in the dosage range studied here.