We studied the distribution of neuropeptide Y (NPY) immunoreactivity in the infundibular nucleus and the hypophysis of the chimpanzee, gorilla, and orangutan. Using antibodies developed in rabbit against synthetic porcine NPY, we found numerous NPY-immunoreactive neuronal somata in the infundibular nucleus; this nucleus was also filled with short NPY-positive processes and an abundance of punctate structures that could be indicative of synaptic terminals. Numerous varicose NPY-positive fibers were concentrated in the upper infundibular stem in association with capillary loops of the portal vasculature and with the long portal vessels. Bundles of long varicose fibers ran down the infundibular stem, some appearing to terminate in the lower stem in the vicinity of short portal vessels. The bulbous infundibular process contained only sparsely distributed fibers; they were mostly concentrated near vessels at the border between the infundibular process and the anterior pituitary gland, where the fibers often terminated in a spray-like fashion near blood vessels. No NPY immunoreactivity was seen in the anterior pituitary gland. These results provide anatomical evidence for the release of NPY into the portal vasculature of great apes.