In the long-term ovariectomized rat the secretion of LH has a pulsatile character. In such rats no difference was observed between morning and afternoon LH secretion. The administration of phenoxybenzamine, an chi-adrenergic blocker, resulted in depressed plasma LH levels. chi-Methyl-tyrosine (chi-MT), an inhibitor of tyrosine hydroxylase had no effect on plasma LH levels, whereas bis(4methyl-1-homopiperazinil-thiocarbonil) disulphide (FLA 63), an inhibitor of dopaminic-beta-hydroxylase, induced decreased plasma LH levels and disappearance of the pulsations. The same effect was observed after the administration of apomorphine, a dopaminic receptor stimulating drug, whereas the administration of 1-hydroxy-3-amino-pyrrolidone-2 (HA-966), which blocks dopamine release, significantly raised plasma LH levels. Scopolamine, a cholinergic muscarinic receptor blocking drug, had no effect on plasma LH levels, whereas mecamylamine, a cholinergic nicotine receptor blocking agent, decreased them. These results are consistent with the hypothesis that the pulsatile release of LH in the long-term ovariectomized rat is caused by the stimulating activity of adrenergic and cholinergic, probably nicotinic, systems and the inhibitory activity of a dopaminergic system.