Experiments were conducted to determine if endogenously produced beta-endorphin and met-enkephalin exert a physiological inhibition on luteinizing hormone-releasing hormone (LHRH) release in the central nervous system of sheep. Twenty-two mature ewes were implanted with unilateral guide tubes, through which matched infusion cannulae could be inserted without discomfort once daily for intracerebral (i.c.) infusion of three anti-opioid treatments: naloxone (50 micrograms in 20 microliters), sheep antisheep beta-endorphin (ABE; 20 microliters of 1:25) or sheep anti-met-enkephalin (AME; 20 microliters of 1:25) and of two control treatments: nonimmune sheep serum (20 microliters of 1:25) or sheep antiporcine thyroglobulin (20 microliters of 1:25). To detect abrupt disinhibition of LHRH release by anti-opioid treatments, serum luteinizing hormone (LH) was quantified at 10-min intervals for 1-2 h before and after each i.c. infusion. Complete trials consisted of 3-4 different anti-opioid or control i.c. infusions once daily at a single site over a period of 2-3 days during the luteal phase of recurring estrous cycles. Results were statistically evaluated within each ewe since complete trials were replicated 2-5 times within each ewe and because no 2 ewes could have i.c. infusions in identical locations. Anatomical generalizations were possible when LH responses to anti-opioid treatments were similar for several ewes with i.c. infusion sites in comparable brain regions. However, it was not possible to make such generalizations when infusion sites were not comparable in other ewes.(ABSTRACT TRUNCATED AT 250 WORDS)