The neuroendocrine regulation of reproduction will be studied in the domestic cat using a radioimmunoassay system for luteinizing hormone (LH), estrogen and progesterone. The patterns of these hormones during polyestrus, pseudopregnancy and pregnancy will be described, and particular emphasis will be placed on the role of single or multiple mating as the primary stimulus for preovulatory LH release. In ovariectomized cats the effects of ovarian steroids (estrogen and progesterone) on LH secretion will be assessed, and the interrelationship between serum steroid concentrations and external stimuli will be explored, using LH release as an endpoint for monitoring their interaction. Attempts will be made to determine the role of the central nervous system in such responses, as indicated by the ability of anesthetics and a potent neurotoxin to block the effects of various stimuli on LH release and the ability of exogeous LHRH to replicate the proposed effects of multiple matings on pituitary gland responsiveness.