The effect of nifedipine on antipyrine ( AP ) disposition was evaluated in 10 patients with essential hypertension. The disposition were measured with high perfomance liquid chromatography before and after 5d nifedipine treatment. The results showed that APt_1/2 and CL_AP were 14.88?3.1h and 31.29?5.9 ml/min respectively before treatment; APt_1/2 and CL_AP were 14.37?3.1 h and 32?6 ml/min after treatment. There were no significant differences for both parameters between the pre-treatment and after-treatment. The results showed there was no effect of nifedipine on AP disposition in patients with essential hyper ension in vivo. Namely, activation of hepatic microsomal enzymes for oxidative metabolism was not affected by nifedipine.