The purpose of this work was to assess whether a single intracavernous injection (ICI) of a low dose of the combination of papaverine-phentolamine is replaceable by a high dose of the oral erectogenic agent sildenafil as mode of stimulation during pharmaco-penile duplex ultrasonography (PPDU). Eleven patients with complaints of erectile dysfunction were included in a crossover study. With an interval of two weeks the patients were exposed to ICI with papaverine/phentolamine (3.75 mg/0.125 mg) and oral administration with sildenafil (100 mg) preceding PPDU. Five patients started with ICI. Six patients started with sildenafil. In the sildenafil stimulation mode, visual erotic stimulation (VES) was used to initiate erection. VES was applied by personal LCD monitor. Cut-off values to define sufficient arterial response were: peak flow velocity (PSV) >25 cm/s and acceleration time (AT) <72 ms. Cut-off value to define sufficient veno-occlusion was a resistance index > or =1.00. Statistical analysis of PPDU parameters shows no significant difference between the two modes of stimulation for arterial response (PSV, AT), whereas the resistance index, as a parameter of veno-occlusive response was significantly higher in the sildenafil mode. This finding is confirmed in the clinical translation of the results: two patients with an insufficient arterial response to ICI had a sufficient arterial response to sildenafil and only one patient showed an insufficient arterial response following sildenafil, whereas the response following ICI was sufficient. Analysis of veno-occlusive responses shows remarkable differences between both modes of stimulation. Whereas following the administration of sildenafil all veno-occlusive responses were classified as sufficient, seven patients showed an insufficient veno-occlusive response following ICI. As mode of stimulation in PPDU, high dose sildenafil yields significantly less false positive diagnoses of 'veno-occlusive dysfunction' than intracavernous injection of the combination papaverine/phentolamine. No difference was found in the quality of the arterial response. Based on this study we conclude that sildenafil may replace ICI as mode of stimulation during PPDU.