Pharmacokinetics and pharmacodynamics of captopril were studied in 5 continuous ambulatory peritoneal dialysis (CAPD) patients (including 2 hypertensive patients) after single oral administration of 50 mg captopril. The pharmacokinetic parameters for plasma free unchanged captopril were time to maximal concentration 1.1 +/- 0.3 h, maximal plasma concentration 387 +/- 75 ng X ml-1, elimination half-life 1.0 +/- 0.3 h, and the area under the concentration-time curve 711 +/- 144 ng X h X ml-1. For plasma total captopril (the sum of free unchanged captopril and its disulfide compounds) the values were time to maximal concentration 3.5 +/- 0.6 h and maximal plasma concentration 2,777 +/- 429 ng X ml-1. Captopril was detected in the dialysis fluid in all CAPD patients. Blood pressures in the 2 hypertensive CAPD patients were lower at 24 h after than before captopril administration. These results suggest that captopril may be eliminated by CAPD. In addition, there is a possibility that the antihypertensive effects of captopril may be prolonged in hypertensive CAPD patients.