To assess the pharmacokinetics parameters of test drug (sildenafil citrate, 100 mg) with referenceViagra®(sildenafil citrate, 100 mg tablet) in healthy male volunteers. An open label, balanced, randomized, two-treatment, two-sequence, two-period, crossover, single-dose bioequivalence study was conducted in healthy adult male subjects, under fasting conditions.Twelve healthy subjects were enrolled in a single-centre, randomized, single-dose, open-label, 2-way crossover study, with a minimum washout period of 7 days. Plasma samples were collected up to 24.0 h postdosing. Concentrations of drugs weredetermined by using a validated LC-MS/MS method. The pharmacokinetics parameter for the reference R and test T for sildenafil was as follow: t1/2 was 2.77 (±1.14) and 2.69 (±0.41) h; Tmax was 0.94 (±0.0.48)h and 0.94 (±0.56) h; Cmax was 607.02 (±156.36) ng/ml and 614.74 (±197.42)ng/ml; AUC0-t was 1988.80 (±676.68) ng.hr/mland 1648.02 (±378.68) ng.hr/ml. Elimination rate constant (Kel) for these products were calculated as 0.28 (±0.08) and 0.26 (±0.04) hrs-1 respectively(for R and T). For piperazine n-desmethyl sildenafilthe pharmacokinetics parameter for the reference R and test T was as follow: t1/2 was 3.74 (±1.47) and 3.99 (±1.59) hrs; Tmax was 1.25 (±0.58) hand 01.35 (±0.94) h; Cmax was 61.76 (±29.93) ng/ml and 69.00 (±29.31) ng/ml; AUC0-t was 304.06 (±179.34) ng.hr/ml and 280.66 (±175.71) ng.hr/ml. Elimination rate constant (Kel)for these products were calculated as 0.22 (±0.08) and 0.20 (±0.08) hrs-1 respectively for (R and T).