The neurons which synthesize and release luteinizing hormone-releasing hormone (LHRH), are hypothesized to originate in the epithelium of the medial olfactory pit and to migrate into the brain along a scaffolding made up of neural cell adhesion molecule (NCAM)-immunoreactive branches of the terminal and vomeronasal nerves. These LHRH neurons, studied by immunocytochemical and autoradiographic procedures, were found to originate within a very short period of embryogenesis, specifically day 10, in mice, and to follow a remarkably ordered spatiotemporal course along the migration route into the brain. The purpose of the present experiments was to determine whether perturbation of the NCAM-immunoreactive migration route, at a particular time in development, would arrest the migration of LHRH neurons into the brain. We found that a 1 microliter injection of antiserum to NCAM into the area of the olfactory pit, on day 10 of embryogenesis, significantly reduced the number of LHRH-immunoreactive neurons seen in the epithelium of the medial olfactory pit, with a concomitant significant reduction in the number of LHRH-immunoreactive cells seen outside of the placode, on the migration route. These results confirm our initial hypothesis that LHRH neurons migrate from the epithelium of the olfactory pit to the brain and indicate that NCAM plays a causal role in this phenomenon.