The antihypertensive effect of felodipine was examined in various hypertensive animal models. In spontaneously hypertensive rats, felodipine administered singly at 0.1-1.0 mg/kg (p.o.) had a dose-dependent antihypertensive effect. Nifedipine was effective at 1 mg/kg. In the repeated oral administration experiment, both the maximum decrease in blood pressure and duration of the effect increased gradually and reached steady levels at 3 weeks of administration, which were maintained thereafter. Similar results were noted with nifedipine, but felodipine was longer-acting (4-6 hr) in the steady state than nifedipine (1-2 hr). No development of tolerance was observed during the administration period. In DOCA-salt and renal hypertensive (2K1C) rats, felodipine at 0.1-0.5 mg/kg (p.o.) was superior to nifedipine in the maximum decrease in blood pressure and duration of the effect. Felodipine up to 1 mg/kg (p.o.) caused no significant heart rate increase in any rat model. In renal hypertensive (2K2C) dogs given felodipine at 0.2-0.5 mg/kg (p.o.), the effect lasted for 2 hr after injection. This felodipine effect was stronger and longer lasting than the nifedipine one. At 0.5 mg/kg of felodipine, the heart rate was transiently increased. The present results show that felodipine has a stronger and long-lasting antihypertensive effect than nifedipine in the hypertension models.