The intravenous (i.v.) administration of opioids to neonates is a common method of providing analgesia in the intensive care setting. This paper reviews and critiques the studies that have investigated this intervention. The studies are grouped into four major areas: pharmacokinetic studies; i.v. opioids for anesthesia; i.v. opioids for sedation or analgesia in mechanically ventilated neonates; and cardiorespiratory effects of i.v. opioids. An attempt is made to synthesize current knowledge about the analgesic effects and side effects associated with the use of i.v. opioids in neonates. The intent is to stimulate additional research on the management of neonatal pain using opioid analgesics.