Pharmacokinetics of [14C]omeprazole and its metabolites were studied after single intravenous and oral doses of 20 and 40 mg, respectively, to 12 patients with chronic renal insufficiency. Blood samples for determination of total radioactivity, omeprazole, OH-omeprazole, sulfone, and sulfide were taken for 24 hours. Urine was collected over 96 hours for determination of total radioactivity and during the first 24 hours for additional assay of omeprazole and metabolites. The mean systemic availability was 70%. The mean plasma t1/2 of omeprazole was 0.6 hours. Unchanged omeprazole was not measurable in urine. Derived pharmacokinetic constants of intact omeprazole were within the range of those reported in healthy individuals. The accumulated 24-hour excretion of radioactive metabolites was related significantly to creatinine clearance. The cumulative excretion of total radioactivity in urine over 96 hours in percent of given dose varied between 25% and 83%.