The effects of $Ca^{2+}-antagonist$, cinnarizine, on the antihypertensive effects of propranolol and metoprolol were investigated in normal cat (i. v.) and SHR (p. o.). Cinnarizine increased the antihypertensive effect of propranolol, but not of metoprolol. It inhibited the heart rate decreasing effects of propranolol and metoprolol slightly. It decreased the norepinephrine-induced blood pressure increasing effect and isoproterenol-induced blood pressure decreasing effect when coadministered with metoprolol orally for 4 weeks in SHRs.