In conscious renal-hypertensive dogs (one kidney Grollman type) oral administration of 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid-bis-(2-propoxyethyl)-ester (niludipine, Bay a 7168) (1 and 3 mg/kg) produced a rather prompt fall of blood pressure and an increase in heart rate. With 3 mg/kg p.o. of niludipine a fall of blood pressure was marked at its peak effect attained about 45 min after dosing and lasted about 3 h. Prior administration of propranolol (30 mg/kg p.o.) greatly prevented an increase in heart rate accompanying the fall of blood pressure produced by 3 mg/kg p.o. of niludipine but was of no effect on the antihypertensive action. These results, taken together with previous results indicating niludipine to have a potent coronary vasodilator action, suggest that niludipine will be useful as an antihypertensive drug, especially when hypertension is associated with ischemic heart disease or when the reduction of blood pressure is urgent. Combined use of niludipine with a beta-adrenergic blocking agent is recommended.