The experience with the administration of intraventricular morphine for the control of malignant pain in 197 patients is analyzed. Small doses of morphine injected via a ventricular reservoir provided satisfactory control of otherwise intractable pain in terminal cancer patients. Complete analgesia together with a favourable behavioral response was obtained without noticeable neurological changes or side-effects annoying or severe enough for the patients to discontinue therapy. Tolerance was much less marked than with parenteral opiates. Chronic intraventricular therapy can be safely performed on an outpatient basis by injecting the opiate once or twice a day. The method may be improved by using refillable continuous-infusion devices and new drugs able to retain the analgesic effects of morphine while eliminating the unwanted ones.