The calcium antagonist nifedipine (Adalat) was administered to 60 patients with essential hypertension and investigations were performed on acute and chronic hypotensive effects. The following results were obtained: 1. Acute hypotensive effects: Nifedipine (20 mg) was either orally or sublingually administered. Following oral administration, significant hypotensive effect was attained 20 min after administration and the maximum hypotensive response was obtained 2-4 h after administration. In cases of sublingual administration, significant hypotensive effect was notable 5 min after administration and blood pressure reached the lowest level 2-3 h after administration. The hypotensive effects lasted for a relatively longer period and significantly lower blood pressure than the control level was observed even 3 h after administration. 2. Chronic hypotensive effects: Nifedipine (30-60 mg/d) was orally administered consecutively. Significant hypotensive effect was attained in and after the 4th week of administration. The yearly changes in the long-term administration cases over 3 years demonstrated significant hypotensive effects. The cases who did not respond to single administration of thiazides or beta-blockers exhibited significant hypotensive response by the combined use of nifedipine. 3. Change in heart rate: In the acute study, heart rate increased after nifedipine administration and lasted for several hours. In the long-term administration cases, the changes in heart rate were not significant. 4. Side effects attributable to nifedipine such as headache in 2 cases, facial flushing, palpitation, warm sensation and nausea in 1 case each were observed early after the administration but there were no cases in whom administration was discontinued due to these side effects.