Objectives. Anxiety and apprehension may negatively influence the erectile response to the first intracavernous injection with vasoactive agents. This may result in too many false-positive diagnoses of vascular insufficiency if the first injection ever made in a patient is used for color Doppler duplex sonography (CDS) evaluation.

Methods. One hundred sixty-eight consecutive patients (aged 18 to 75 years) with erectile dysfunction underwent a standardized evaluation, including the intracavernous injection test (ICIT) stimulated with 10 μg prostaglandin E₁. Responses were recorded on a four-point scale: no response = 0, tumescence = 1, rigidity sufficient for intercourse = 2, full erection = 3. ICIT was repeated after 10 days and combined with CDS. The clinically assessed response to ICIT was correlated with end-diastolic flow velocity.

Results. Of 168 patients, 114 (68%) responded equally to the first and second ICIT, but 45 (27%) had an improved response, from tumescence to full erection in the second test (P <0.0001); in 9 (5%), the response deteriorated. The overall mean response was 1.6 (95% confidence interval 1.5 to 1.7) and 1.9 (95% confidence interval 1.7 to 2.0) (P <0.0001) for the first and second test, respectively. Of 168 patients, 89 (53%) responded with erections sufficient for intercourse when tested the first time and 104 (62%) did so after the second injection.

Conclusions. Erectile response to diagnostic intracavernous injection of prostaglandin E₁ significantly improved in the second compared with the first test. Therefore, cautious interpretation of CDS is advised when patients are injected for the first time because too many false-positive tests may result.