1 The effect of verapamil pre-treatment on the pharmacokinetics and metabolism of antipyrine was studied in eight healthy male volunteers. 2 The oral clearance of antipyrine was decreased from 2.18 to 1.95 1 h-'1 (P < 0.01) by verapamil (80 mg three times daily for 2 days prior to antipyrine administration and 2 days following) while half-life was increased from 13.2 to 15.6 h (P < 0.01). 3 The urinary excretion of norantipyrine, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine was decreased by 19.2%, 23.1% and 16.7% respectively (P < 0.05) in the presence of verapamil. In addition, the rate constants for formation of each of these metabolites were significantly decreased by an average of approximately 30%. 4 These results suggest that verapamil is capable of inhibiting oxidative metabolism, a finding which could be of clinical significance for drugs highly dependent upon pathways such as those inhibited in this study for elimination.