Drug metabolizing capacity is generally reduced in the elderly, and physical exercise has been reported to increase drug oxidative metabolism. The purpose of this investigation was to study the effects of engagement in a program of regular physical exercise on the clearance and metabolite excretion of antipyrine, a marker of oxidative metabolism, in elderly subjects. The saliva clearance of antipyrine and the production clearances of antipyrine metabolites were studied in 37 elderly women (mean age 66 years). Subjects attended 60-min sessions three times a week for 12 weeks. Each session consisted of both aerobic (training of cardiorespiratory capacity) and nonaerobic (training of muscular strength/endurance and flexibility/coordination) exercises performed at 50-75% of maximum oxygen uptake. Antipyrine was administered orally and pharmacokinetic parameters were obtained from saliva and urine samples. After 3 months of participation in the exercise program, salivary antipyrine clearance was significantly increased by 17% mean (SEM) 0.42 (0.02) vs 0.36 (0.02) ml/min/kg; P < 0.05) and the half-life of antipyrine was significantly reduced by 18% (17.9 (1.1) vs 22.3 (1.3) h; P < 0.05). No significant change with exercise was observed in the renal clearance of antipyrine or in the norantipyrine formation clearance, but significant increases were found for hydroxymethylantipyrine [42 (5) vs 32 (4) microl/kg/min; P < 0.05; +31%] and 4-hydroxyantipyrine [243 (18) vs 194 (17) microl/kg/min; P < 0.05; +25%] formation clearances. These findings indicate that regular exercise leads to increased disposition of antipyrine in the elderly and that the main metabolic pathways of the compound are changed differentially.