Studies were performed to determine whether the postovulatory secretion of FSH in the rabbit is an LHRH-mediated event. Does were mated and then injected at 12 and 18 h postcoitum with pentobarbital (30 mg/kg BW), an agent known to block endogenous LHRH release. The injection of this barbiturate had no measurable effect on the postovulatory FSH secretion pattern. Administration of the LHRH antagonist [Ac-D-p-C1-Phe1,2, Phe3, D-Arg6, D-Ala10]LHRH (0.5 mg/doe) prevented all gonadotropin release in response to LHRH injection (10 micrograms/kg BW). When this same dose of the antagonist was injected at 18 h postcoitum, the postovulatory FSH secretion pattern was unaffected. Finally, to prove that the pituitary was sensitive to LHRH at 18-h postcoitum, LHRH (10 micrograms/kg BW) was injected into rabbits mated 18 h earlier; this treatment led to a marked increase in FSH secretion showing that the pituitary is responsive to LHRH at this time. The results of this study show that two drugs which block LHRH-mediated gonadotropin release have no effect on the postovulatory secretion of FSH and support the concept that this episode of FSH secretion occurs via a pathway which does not include the hypothalamic secretion of LHRH.