Aim:To determine the effect of sildenafil citrate on the nocturnal penile erections (i.e.time to onset,the duration oferection,and the interval between first and second erections) of healthy young men.Methods:Twenty-two potentmen,23-29 years old,were recruited for the study.All subjects completed three sessions over consecutive nightsusing the RigiScan monitoring device (Dacomed,Minneapolis,USA).After a first night of adaptation,night 2 recordswere their baseline values,and on night 3 they received 100 mg of sildenafil citrate.Statistical comparisons were donebetween the second and third night data.Results:The mean time to onset of the first erection with sildenafil citratewas (34±18) min,whereas it was (74±24) min (P<0.001) without sildenafil citrate.The number of erectionsobserved during the first 5 h after sildenafil citrate medication was 3.6±0.5 in contrast to 2.4±0.5 with no medica-tion (P=0.001).The interval between first and second erections was shorter with sildenafil citrate:(52±26) min vs.(85±34) min (P=0.01).The duration of the last erection was statistically significantly longer with the sildenafilcitrate:(64±33) min vs.(42±28) min (P<0.01).Conclusion:Healthy young men achieved erection within34 min after sildenafil citrate administration,which is shorter than the 1 h interval proposed by the manufacturer.Theinterval between the first and second erections was shorter and the duration of the last nocturnal erection was longer.(Asian J Androl 2005 Dec;7:395-398) Aim: To determine the effect of sildenafil citrate on the nocturnal penile erections (ie time to onset, the duration of erection, and the interval between first and second erections) of healthy young men. Methods: Twenty-two potentmen, 23-29 years old , were recruited for the study. All subjects completed three sessions over consecutive nights using the RigiScan monitoring device (Dacomed, Minneapolis, USA). After a first night of adaptation, night 2 recordswere their baseline values, and on night 3 they received 100 mg of Results: The mean time to onset of the first erection with sildenafil citrate was (34 ± 18) min, yet it was (74 ± 24) min (P <0.001) with without sildenafil citrate sildenafil citrate. The number of erectionsobserved during the first 5 h after sildenafil citrate was was 3.6 ± 0.5 in contrast to 2.4 ± 0.5 with no drug- tion (P = 0.001). The interval between first and second erections was shorter with sildenafil citr ate: (52 ± 26) min vs. (85 ± 34) min (P = 0.01). The duration of the last erection was significantly longer with the sildenafilcitrate: (64 ± 33) min vs. (42 ± 28) min (P <0.01) .Conclusion: Healthy young men achieved erection within 34 min after sildenafil citrate administration, which is shorter than the 1 h interval proposed by the manufacturer.The interval between the first and second erections was shorter and the duration of the last nocturnal erection was longer. (Asian J Androl 2005 Dec; 7: 395-398)