Fifty-five patients with pain associated with cancer were selected for long-term treatment with epidural morphine. Patients who had more than one type of pain within the same region were specially analysed concerning differential analgesic effects of the treatment, i.e. the patients served as their own control. Twenty-eight of the 55 patients became pain free. In 21 patients alleviation of pain was complete only for one or two of several types of pain within the same area with a certain dose of epidural morphine. In six patients the treatment failed. An analysis revealed that the best response was obtained when the pain was continuous and originated from deep somatic structures. In co-existing continuous visceral pain or intermittent somatic pain originating e.g. from a pathological fracture, the outcome of the treatment was variable. Cutaneous pain, pain classified as neurogenic, and intermittent pain due to intestinal obstruction was only occasionally relieved. Ten of the patients had co-existing pain of non-malignant origin and none of them was helped for that pain. The variable response to epidural morphine may indicate that different types of pain-producing stimuli engage different kinds of receptors which differ in affinity to morphine in the spinal fluid; it is also possible that some pain-mediating systems are non-responsive to opiates.