Parasympathetic and sympathetic pathways may be assessed by using different electrophysiologic tests. Sympathetic skin potentials (SSP) are elicited with peripheral electrical stimulation (e.g. median nerve or pudendal nerve). SSP are recorded from the skin of the hand and foot and from the genital skin. Skin responses were always obtained from normal volunteers. Absence of SSP is one of the earliest findings in neurogenic impotence. Electromyography of corpora cavernosa is described with a new method. A new corpora cavernosa response to pudendal nerve stimulation is described. This test appear to have application in the evaluation of neurogenic impotence.