The analgesic effects of epidural morphine were evaluated on various types of cancer-related pain in forty-eight adult patients. Epidural morphine injections were given via an epidural catheter introduced to an epidural level corresponding to the pain area. Pain relief was classified as excellent, fair, or poor by subjective scoring and by the subsequent need for systemic analgesics. Thirty-two patients of all the patients became pain-free. In sixteen patients, pain relief was complete only for one or two of various types of pain with a certain dose of epidural morphine, The best result was obtained when the pain was continuous and originated from deep somatic structures. Based on the results, the ranking order of different types of cancer pain with regard to their susceptibility to epidural morphine was as follows: 1) Continuous somatic pain 2) Continuous visceral pain 3) Intermittent somatic pain 4) Intermittent visceral pain The differential effects of epidural morphine on cancer-related pain may suggest that various types of noxious stimuli involve different kinds of opioid receptors which differ in affinity to morphine, and that there are some pain-mediating systems which function independently of opioid mechanisms.