The aim of the present study was to investigate the influence of prolonged physical exercise on hepatic metabolism. An oral antipyrine loading test (15 mg/kg body weight) was carried out on 24 healthy male subjects: 8 controls, 8 sprinters (anaerobic activity), 8 long distance runners (aerobic activity). Antipyrine clearance resulted to be significantly higher in athletes vs. controls, without a significant difference between the two groups of athletes. These results put forward the importance of the degree of physical activity (1) for the evaluation of antipyrine-loading-test results as expression of liver function and (2) whenever drugs with a low therapeutic index are used in athletes.