Oxytocinergic neurons of the paraventricular nucleus (PVN) of the hypothalamus have been implicated in modulating male sexual responses in rats. Previous investigators have shown that cerebrospinal fluid concentrations of oxytocin (OT) increased after ejaculation and that intraventricular administration of OT and electrolytic lesions of the PVN increased temporal measures of male sexual behavior. Recently, we have demonstrated that OT-immunoreactive neurons in the parvocellular subnuclei of the PVN project to lower levels of spinal cord. In the present study, N-methyl-D-aspartic acid lesions, which have been shown to destroy parvocellular PVN neurons while leaving magnocellular neurons intact, were used to evaluate the role of parvocellular neurons on male copulatory behavior and seminal emissions. OT-immunoreactive fibers were reduced in the lower lumbar spinal cord (L5-L6) following N-methyl-D-aspartic acid lesions in the PVN. This reduction was associated with a significant decrease in seminal emission at the time of ejaculation, but mount, intromission and ejaculatory latencies were unaffected.