Substance P-like immunoreactive nerve fibers have been found in the pars distalis of the adenohypophysis in the monkey, dog, and rat. Calcitonin gene-related peptide-like immunoreactive nerve fibers have also been identified in the dog and rat. The peptidergic fibers are closely related to the glandular cells with synaptic contacts demonstrated between them. It is suggested that neural factors may be directly involved in the regulation of the activities of the anterior pituitary.