A single dose complete crossover study of a combined dosage form of Captopril (25 mg) and hydrochlorthiazide (12.5 mg) marketed in India was carried out in eight healthy male volunteers. The data obtained was compared with the data obtained for a second study conducted by administering captopril alone. Plasma samples were analysed for captopril using the indirect method of Angiotensin I radioimmunoassay (RIA). Hydrochlorthiazide in plasma was analysed by HPLC. Pharmacokinetic parameters such as Cmax, Tmax, AUC(0-t), AUC(0-∞), AUMC(0-24), AUMC(0-∞), MPT(0-t), MPT(0-∞), halflife (1) and halflife (2) were determined by nonlinear least square regression analysis computer program PSTRIP and were subjected to statistical analysis. The study showed that hydrochlorthiazide did not alter the pharmacokinetics of captopril. The study showed no undesirable interaction between the two drugs.