Infusion pharmacocavernosometry and nocturnal penile tumescence findings were compared in 50 men with erectile dysfunction of either organic or psychogenic etiology. Of the men 29 had abnormal and 21 had normal nocturnal penile tumescence. Infusion pharmacocavernosometry parameters (equilibrium pressure, maintenance flow rate and 30-second pressure fall) were compared to nocturnal penile tumescence status (normal versus abnormal). When traditional normal values were used for infusion pharmacocavernosometry parameters poor correlation with nocturnal penile tumescence status was found. When new cutpoints for infusion pharmacocavernosometry parameters were chosen a stronger correlation was noted. This study suggests that when vasoactive drugs are injected intracavernously for diagnostic purposes, anxiety and/or the absence of sexual stimulation following the injection may prevent complete cavernous smooth muscle relaxation resulting in falsely abnormal values. Therefore, over reliance on infusion pharmacocavernosometry as a single test for evaluation and treatment decisions concerning erectile dysfunction should be avoided.