The distribution of immunoreactive LH in the brain of the white-footed mouse (Peromyscus leucopus) was determined using immunocytochemical procedures. Immunoreactive fibers are located in the hypothalamus, preoptic area, septum and amygdala. Stained cell bodies are seen in the arcuate nucleus and preoptic area. Gonadectomy enhances staining for LH in the brain.