Attempts were made to destroy selectively the arcuate nucleus with radiofrequency current in adult female rhesus monkeys as a 1st step in identifying the areas of the mediobasal hypothalamus (MBH) that are responsible for the neural control of gonadotropin secretion in this species. Extensive or complete destruction of the arcuate region was produced in 3 animals, and in 2 of these the lesion was confined primarily to the arcuate region and the dorsal aspect of the posterior median eminence. These lesions resulted in the cessation of LH [luteinizing hormone] and FSH [follicle stimulating hormone] secretion and blocked the positive feedback action of estradiol on gonadotropin release, but did not appear to influence grossly basal thyroid and adrenocortical function, or to abolish GH [growth hormone] discharge in response to insulin hypoglycemia. Adenohypophysial infarcts were not observed, and exogenous LHRH [luteinizing hormone releasing hormone] and TRH [thyrotropin releasing hormone] induced marked discharges of the appropriate anterior pituitary hormones. In 2 additional animals with large hypothalamic lesions, destruction of the arcuate region was incomplete. In this group only partial inhibition of gonadotropin secretion was observed. LH and FSH secretion did not appear to be influenced in 1 animal bearing a large MBH lesion that entirely spared the arcuate region. Although serum prolactin remained at pre-lesion control levels after placement of the 2 relatively discrete lesions confined to the arcuate region, unambiguous increases in the secretion of this hormone were observed when the area of destruction encompassed tissue anterior and/or dorsal to the arcuate region. The arcuate region may be the primary structure mediating the hypothalamic control of gonadotropin secretion in the rhesus monkey. In this species, the regions of the MBH involved with the regulation of gonadotropin release and those which control prolactin secretion apparently are anatomically distinct.