Lesions were made in various hypothalamic and preoptic regions in sexually mature female and male goldfish. Destruction of the pituitary stalk, and lateral anterior hypothalamic tract areas caused ovulation and increased serum gonadotropin levels. Destruction of the entire preoptic region or a major part of the anterior nucleus preopticus periventricularis also caused ovulation and increased serum GtH levels. Lesions in other locations were ineffective. The results indicate that a gonadotropin release-inhibitory factor (GRIF) probably originates in the anterior preoptic region, and reaches the pituitary via pathways in the lateral preoptic and lateral anterior hypothalamic regions, and the pituitary stalk. The preovulatory surge of gonadotropin secretion may be regulated by release from inhibition exerted by GRIF in goldfish.