To assess the safety, efficacy, and use of continuous iv infusion (CI) of opioids for cancer pain, we reviewed the clinical experience of 36 patients who received 46 CIs. CI was always preceded by a period of repetitive dosing of opioids. Morphine was used in 36 CIs, methadone in four, hydromorphone in four, oxymorphone in one, and levorphanol in one. Mean doses during CI were the morphine equivalent of 17 mg/hour (range, 0.7-100) at the start, 69 mg/hour (range, 4-480) at the maximum, and 52 mg/hour (range, 1-480) at termination. Pain relief was acceptable during 28 CIs, unacceptable during 17, and unknown during one. There were few toxic effects other than sedation. Twenty-five patients died, 12 resumed im or oral opioids, six continued CI with a different opioid (yielding analgesia in two), and outcome was undetermined in three. This review suggests that (a) CI is safe, (b) analgesia may require rapid escalation of infusion rates, (c) patient response varies and lack of acceptable analgesia may occur in up to one-third, (d) ineffective CI with one drug may be followed by success with another, (e) CI should be preceded by a period of repetitive iv boluses with the same drug, and (f) guidelines can be developed which incorporate pharmacokinetic principles.