The erectile response to intracavernosal injection (ICI) of smooth muscle relaxants is often impaired in men with presumed psychogenic erectile dysfunction.This study tests the hypothesis that such impairment results from stress-related increase in circulating norepinephrine (NE). Fifty-nine men with erectile dysfunction had their nocturnal penile tumescence (NPT) monitored over 2 nights, and ICI of 10 microg prostaglandin E1was given on the second morning. Psychometric and neuroendocrine measures of stress, including plasma and urinary catecholamines, were taken on both mornings. Inhibition of the ICI response was determined by the difference between NPT and ICI responses, and two groups of "high inhibition" and "low inhibition" men were compared. The high inhibition group showed higher "Trait" and "State" anxiety and a neuroendocrine profile of higher initial cortisol and lower plasma catecholamine levels than the low inhibition group. These differences were evident on both mornings and hence were not specifically related to the ICI. There was no support for the hypothesis that inhibition of response to ICI results from increased circulating NE, though the possibility that increased NE release occurred specifically in the erectile tissues could not be excluded.