A neuroleptic agent, haloperidol, administered orally to rats induced delayed implantation which could be prevented by a single injection of oestrone, HCG or PMSG on Day 4 of pregnancy implying a central action of haloperidol. In view of the known ability of this agent to interfere selectively with dopaminergic transmission, it is inferred that gonadotrophin release for the oestrogen surge preceding implantation in rats is regulated by a catecholaminergic pathway in the hypothalamus.