Neurons of the rat major pelvic ganglia provide innervation to the pelvic organs and external genitalia. In these ganglia, a subpopulation of neurons containing either nitric oxide synthase or vasoactive intestinal peptide or both molecules, is involved in penile erection. The androgen dependence of penile erection is a well established fact. After castration, decreased testosterone levels have been documented to produce erectile dysfunction possibly resulting from functional alterations in major pelvic ganglion neurons. It was therefore of interest to investigate the presence of androgen receptor within these ganglionic neurons. By using immunohistochemistry and a retrograde labeling technique we have demonstrated that the androgen receptor is present in about 40% of neurons of the major pelvic ganglion innervating the corpora cavernosa of the rat penis. In the major pelvic ganglion, 87% and 81% of the neurons labeled with the fluorescent dye Fast Blue from the penis contained nitric oxide synthase-like immunoreactivity and vasoactive intestinal peptide-like immunoreactivity, respectively. Androgen receptor was present in 20% of neurons containing vasoactive intestinal peptide-like immunoreactivity and about 40% of those containing nitric oxide synthase-like immunoreactivity. These results suggest that androgens, which are known to modulate penile erection, may regulate nitric oxide synthase and vasoactive intestinal peptide within the major pelvic ganglion via a direct interaction with ganglionic neurons.