The absorption and disposition of single-dose intravenous (i.v.) and oral ranitidine were evaluated in 6 patients undergoing chronic hemodialysis. Ranitidine was given as either 50 mg (0.16 m M) i.v. or 150 mg (0.48 m M) tablets 4 h prior to hemodialysis according to a randomized cross-over design with tests separated by 2 weeks. Following i.v. administration, the peak serum ranitidine concentration was 761 ± 207 µg/l (mean ± SD) and the observed peak after the oral dose was 833 ± 206 µg/l at 3.5 ± 1.2 h. To convert µg/l to µM/1, divide by 314. The terminal elimination rate constants for the i.v. and oral doses were 0.062 ± 0.013 and 0.058 ± 0.004 h<sup>-1</sup>, respectively, with an apparent volume of distribution of 139.6 ± 35.3 liters and total body clearance 8.5 + 1.6 liters/h for the i.v. dose. Hemodialysis clearances during the i.v. and oral studies were 3.2 ± 0.9 and 3.1 ± 1.0 liters/h, respectively, and the mean amount removed by hemodialysis following i.v. administration was 3.9 ± 2.7 mg. The bioavailability of ranitidine was 54.3 ± 13.5%. Based on these single-dose data, a daily oral dose of 150 mg ranitidine in patients with end-stage renal disease should provide a mean ranitidine serum concentration of approximately 350 µg/l with less than 10% of body stores of ranitidine being lost during any dialysis session.