The olfactory placodes generate the primary sensory neurons of the olfactory sensory system. Additionally, the olfactory placodes have been proposed to generate a class of neuroendocrine cells containing gonadotropin-releasing hormone (GnRH). GnRH is a multifunctional decapeptide essential for the development of secondary sex characteristics in vertebrates as well as a neuromodulator within the central nervous system. Here, we show that endocrine and neuromodulatory GnRH cells arise from two separate, nonolfactory regions in the developing neural plate. Specifically, the neuromodulatory GnRH cells of the terminal nerve arise from the cranial neural crest, and the endocrine GnRH cells of the hypothalamus arise from the adenohypophyseal region of the developing anterior neural plate. Our findings are consistent with cell types generated by the adenohypophysis, a source of endocrine tissue in vertebrate animals, and by neural crest, a source of cells contributing to the cranial nerves. The adenohypophysis arises from a region of the anterior neural plate flanked by the olfactory placode fields at early stages of development, and premigratory cranial neural crest lies adjacent to the caudal edge of the olfactory placode domain [Development 127 (2000), 3645]. Thus, the GnRH cells arise from tissue closely associated with the developing olfactory placode, and their different developmental origins reflect their different functional roles in the adult animal.