1. The effects of propranolol and R03-4787, a new beta-adrenoceptor antagonist with a partial agonist activity, have been studied in a blind, cross-over comparison with placebo.
2. In ten patients who completed the study, the two drugs produced a similar reduction in blood pressure; the reduction in heart rate with propranolol was significantly(P0.001)greater than that produced by R03-4787.
3. Plasma renin activity averaged 4.13 ± 1.37 ng h−1ml−1 on placebo, fell to 3.64 ± 1.47 ng h−1ml−1 on propranolol and to 2.50 ± 1.39 ngh−1ml−1 on R03-4787.
4. No correlation was demonstrable between the log plasma concentration of either propranolol or R03-4787 and change in blood pressure.