Penile dynamic colour-coded doppler ultrasonography (CCDU) provides reliable information on both hemodynamic factors, arterial inflow and veno-occlusive mechanism, involved in erectile function. However false negative results may occur due to sympathetic discharge and consequent incomplete smooth muscle relaxation. From March 1994 to February 1996, 150 patients suffering from ED were submitted to penile dynamic CCDU after high-dose (40 micrograms) pharmacostimulation and manual genital stimulation. False negative results occurred only in 3 (2%) patients. This experience suggests that high-dose pharmacostimulation and manual genital stimulation may reduce the occurrence of false negative results, further increasing the diagnostic value of CCDU.