The avidin-biotin-peroxidase technique is proposed for the immunological localization of beta-endorphin in the rat spinal cord. A rabbit specific antibody anti-human beta-endorphin was first obtained and then identified by immunoblotting and incubated with a quick-frozen section of young rat spinal cord. The use of a specific antibody with the immunoperoxidase reaction gave a morphological visualization of the beta-endorphin in the histological sections of the rat spinal cord.