The influence of 2 weeks oral intake of nifedipine (2 x 20 mg) on the oxidative metabolism of antipyrine was investigated in 12 normal volunteers, who had 1050 mg antipyrine solution orally before and after the course of nifedipine. There were no statistically significant differences in the saliva pharmacokinetic parameters of antipyrine on both occassions. However, the metabolite profile of antipyrine in urine showed a significant reduction in the amount of norantipyrine excreted after compared to that before nifedipine administration (16.5 vs 19.6%). This may have implications for drugs that share a similar demethylation pathway with norantipyrine.