The haemodynamic, antianginal and antihypertensive effects of nicardipine, a vascular selective calcium antagonist, were studied in experimental animals. In the canine isolated coronary artery, nicardipine relaxed potassium-induced contraction and suppressed 3,4-diaminopyridine-induced rhythmic contractions more effectively than nifedipine, verapamil or diltiazem. In anaesthetised rats, nicardipine prevented the elevation of ST segment induced by intracoronary injection of methacholine. In anaesthetised dogs, nicardipine produced a greater vasodilatation in vertebral, carotid, and coronary vessels than in mesenteric, femoral, and renal vessels and did not affect myocardial oxygen consumption. In conscious monkeys, nicardipine given intravenously lowered blood pressure and gave rise to reflex tachycardia but did not prolong the A-V conduction time. Nicardipine given orally lowered blood pressure in spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR), and deoxycorticosterone acetate/salt hypertensive rats (DOCA/Salt), as well as in normotensive rats. Long-term treatment with nicardipine given orally for 12 weeks effectively lowered high blood pressure in the three types of hypertensive rats, reduced cardiac hypertrophy in SHR and DOCA/Salt rats, and prevented mortality from stroke in DOCA/Salt rats. Combined treatment with nicardipine and a beta-adrenoceptor blocking agent (indenolol) showed an antihypertensive effect similar to that obtained with nicardipine alone. Conscious renal hypertensive dogs given repeated oral administration of nicardipine for 14 days did not develop tolerance to the hypotensive activity of nicardipine. Under the same conditions, tolerance to hydralazine developed within 4 days.