Abstract
1. In rats, a subcutaneous injection of morphine (2.5 mg/kg) produced hyperthermia which was greatly attenuated by an intraperitoneal injection of physostigmine (0.1 mg/kg), but not of neostigmine (0.08 mg/kg) and promptly reversed by a subcutaneous injection of nalorphine.2. It is concluded that the hyperthermia is a specific response to morphine, central in origin, and the result of diminished acetylcholine (ACh) release from central cholinergic neurones.