The pharmacokinetics of procainamide in patients on continuous ambulatory peritoneal dialysis have been studied. A mean peak plasma concentration of 3.2 +/- 0.6 microgram/ml was achieved about 2 h after a single 500-mg oral procainamide hydrochloride dose. The procainamide elimination half-life ranged from 6.1 to 15.3 h. Apparent oral clearance, 183.7 +/- 63.2 ml/min, was less than half that observed in healthy adults suggesting markedly reduced dosage requirements. Continuous ambulatory dialysis patients exhibit similar procainamide pharmacokinetic parameters as do end stage renal disease patients, most notably a prolonged elimination half-life and reduced oral clearance.