These experiments were undertaken to determine whether neuropeptide Y (NPY) could suppress a prostaglandin hyperthermia in conscious dogs. Prostaglandin E2 (PGE2) (5 micrograms), injected into the lateral cerebral ventricle (ILV), evoked a hyperthermia of approximately 1 degrees C. Addition of ILV NPY (5 micrograms) significantly attenuated the PGE2-induced hyperthermia, whereas pancreatic polypeptide (PP), another member of the PP family peptide, did not. These results provide evidence for a role of NPY on thermoregulation in the dog.