The effects of cinnarizine, $Ca^{2+}-antagonist$, on the antihypertensive effect of coadministered ${eta}-blockers$, propranolol and metoprolol, were investigated in SHR. Drugs were coadministered orally for 4 weeks. Hemodynamic and biochemical changes induced by above drugs were determined to elucidate their mechanism of action. a) Cardiohypertropy of SHR was significantly improved by the treatment of ${eta}-blockers$ as well as combination with cinnarizine and ${eta}-blockers$. b) $Mg^{2+}-contents$ were increased in ventricle and decreased in plasma and aorta in all of the groups, especially in the group of propranolol with cinnarizine. c) c-GMP contents in ventricle were increased when cinnarizine was coadministered with propranolol, and c-GMP contents in aorta were increased when cinnarizine was coadministered with metoprolol, camparing with propranolol or metoprolol alone-treated group. d) Plasma renin activity appeared to be increased in cinnarizine treated alone, but reduced by combination with ${eta}-blockers$. e) Triglycerides and $Na^+$ contents in serum were decreased in the group of metoprolol with cinnarizine, comparing with metoprolol alone-treated group. Increased $K^+;and;Ca^{2+}$excretions in urine by ${eta}-blockers$ were inhibited by cinnarizine, so $Na^+/K^+$ excretion ratios were increased. Diuretic effects was showed in metoprolol alone treated group, but reduced when coadministered with cinnarizine.