The organization of the gonadotropin-releasing hormone (GnRH) system originating from the terminal nerve (TN) neuron in the olfactory bulb was examined immunohistochemically by tracing the changes in the distribution of salmon type (sGnRH) and chicken-II type (cGnRH-II) GnRH fibers after olfactory tract section (OTX) in the female goldfish. Following OTX, which blocks the axonal transport of GnRH from the TN to other brain regions, the density of sGnRH-ir fibers in various brain regions decreased from 7 days to 28 days, with the exception of rather restricted areas surrounding cell bodies in the ventral telencephalon, preoptic area, and hypothalamus. The density of cGnRH-II-ir fibers decreased only in the telencephalon from 7 days to 14 days. In spite of the decrease of GnRH-ir fibers in several brain areas, neither type of GnRH fibers showed marked changes in the pituitary gland during the experiment. These results indicate that the TN GnRH system project fibers to wide brain areas and that most of sGnRH and some of the cGnRH-II-ir fibers in the brain of goldfish are TN origin. Furthermore, the GnRH system that project fibers to the pituitary does not primarily originate from the TN-GnRH system.