Activities of type A monoamine oxidase (MAO), acetylcholine esterase (AChE), and glucose-6-phosphate dehydrogenase (G6PDH) were differentially altered in hormone-sensitive areas of the preoptic-hypothalamic continuum after administration of estrogen and progesterone. Estrogen increased activity of AChE in the bed nucleus of the stria terminalis and activity of G6PDH in the periventricular area (PVE) of the preoptic area, arcuate-median eminence (Ar-ME) and pituitary. Estrogen decreased activity of MAO in the PVE of the anterior hypothalamus, pars lateralis of the ventromedial nucleus and in the Ar-ME. Acute administration of progesterone (1 h) to estrogen-treated females did not further alter estrogen-dependent changes in AChE or G6PDH; however, MAO activity in the ventromedial nucleus and Ar-ME was rapidly increased after progesterone. Without prior estrogen administration, progesterone did not affect MAO activity. Administration of the protein synthesis inhibitor anisomycin prior to progesterone did not antagonize progesterone-dependent increases in MAO. Progesterone added in vitro to homogenates from estrogen-treated but not from untreated females increased MAO activity. The hormonal specificity, time course of effects and anatomical location of the enzymatic changes suggest that some of them may participate in the mediation of gonadal hormone action in the CNS. In particular, changes in MAO activity in the ventromedial nucleus and Ar-ME are consistent with reported effects of these hormones on monoamine turnover which in turn have been suggested to contribute to hormonal regulation of feminine sexual behavior and gonadotropin secretion.