In a randomized, double-blinded study, we evaluated the analgesic effect of ketamine in the management of pain in a surgical intensive care unit after major abdominal surgery. Patients received morphine patient-controlled analgesia with either placebo (Group M) or ketamine (Group K). Morphine was administered with initial loading doses of 2 mg until the visual analog scale (VAS) score was <30 and thereafter with bolus doses of 1 mg and a lockout time of 7 min. Ketamine was administered with an initial bolus of 0.5 mg/kg followed by a perfusion of 2 micro g x kg(-1) x min(-1) during the first 24 h and 1 micro g x kg(-1) x min(-1) during the following 24 h. The 4-h cumulative morphine doses were measured over 48 h. The VAS scores at rest and at mobilization were measured every 4 h during 48 h. A total of 101 patients were enrolled, and 93 were analyzed (41 in Group K and 52 in Group M). VAS scores at rest and at mobilization were similar. The cumulative consumption of morphine was significantly smaller in Group K (P < 0.05). We concluded that small doses of ketamine were a valuable adjunct to opioids in surgical intensive care unit patients after major abdominal surgery.