The pharmacokinetics of omeprazole and its metabolites were studied in 8 healthy elderly volunteers using [14C]omeprazole. In another 6 healthy elderly volunteers, the pharmacokinetics of omeprazole were studied using unlabelled drug. Each volunteer received single doses of omeprazole intravenously (20mg) and orally (40mg) as solutions in a randomized crossover design. The plasma concentrations and urinary excretion of omeprazole and metabolites were followed for 24 and 96h, respectively. The results indicate that the average metabolic capacity of omeprazole is decreased in the elderly compared with that found in earlier studies of healthy young individuals. This was reflected in an increase in bioavailability from 56 to 76%, a reduction in mean systemic clearance by approximately 50% (0.25 L/min) and a prolongation of the mean elimination half-life from 0.7 to 1.0h compared with the young. Despite these findings, the considerable overlap in these parameters between young and old volunteers, together with data from previous pharmacodynamic studies and the wide therapeutic range of omeprazole, indicate that dosage reductions are not needed in the elderly.