A single dose complete crossover study of combined dosage form of Lisinopril (5 mg) and hydrochlorothiazide (12.5 mg) marketed in India was carried out in twelve healthy male volunteers. The study was compared with a standard formulation of lisinopril (5 mg) and hydrochlorothiazide (12.5 mg). Plasma samples were analysed for lisinopril using the indirect method of Angiotensin I radioimmunoassay (RIA).