Pain and its treatment are known to have adverse effects on the organism, including deterioration in myocardial, diaphragmatic, and small bowel function. The provision of adequate intravenous analgesia, and the choice of agent, can ameliorate or exacerbate these manifestations of the stress response. The choice of agent, opioid or non-opioid, has in some respects become more difficult as more information has become available regarding the merits and adverse effects of each. Increased awareness of the frequency of hypoxemia secondary to the opioids' ability to cause an obstructive sleep apnea picture, and the cost efficiency of ketorolac through a reduction in opioid toxicity, contrast with recent studies which suggest that the gastrotoxic and nephrotoxic effects of ketorolac may occur earlier than previously suspected. The suitability of using the dissociative anesthetic agent ketamine in critically ill patients remains to be proven. Ketamine provides intense analgesia at subanesthetic doses. Its centrally mediated sympathomimetic action encourages hemodynamic stability, and it is relatively devoid of respiratory depressant activity. Increasing experience with ketamine outside the operating room has resulted in its successful use in cases of severe bronchospasm and status epilepticus.