Previous research implicates an endogenous central pain inhibitory mechanism in opiate analgesia, analgesia produced by focal electrical stimulation of the brain, and acupuncture analgesia. This investigation evaluates the possibility that analgesia produced by hypnosis is also mediated by such a mechanism. Results suggest that hypnotic analgesia is unlikely to involve this central pain inhibitory mechanism since hypnotic analgesia is not altered by naloxone hydrochloride, a specific narcotic antagonist. Results further demonstrate that the hypnotic procedure used produces an unusually effective and reliable increase in pain threshold. This finding generalizes to the control of clinical dental pain, and suggests that hypnotic pain control is a more widespread phenomenon in the population than has been thought.