["Anaesthesia and surgery are associated with impairment of the immune system expressed as an excessive proinflammatory immune response and suppression of cell-mediated immunity that may affect the course of the postoperative period. Addition of anaesthetic agents capable of attenuating the alterations in perioperative immune function may exert a favourable effect on patients' healing. We have assessed the effect of preoperative administration of a sub-anaesthetic dose of ketamine on the mitogen response and production of interleukin (IL)-1beta, IL-2, IL-6, and tumour necrosis factor (TNF)-alpha by peripheral blood mononuclear cells (PBMCs), as well as natural killer cell cytotoxicity (NKCC) in patients undergoing abdominal surgery.", 'Seventeen patients admitted for elective abdominal surgery were given ketamine 0.15 mg kg(-1) i.v. 5 min before induction of general anaesthesia. Nineteen patients received a similar volume of isotonic saline 5 min before induction of the anaesthesia. PBMCs were isolated from venous blood before and 4, 24, 48, and 72 h after operation for IL-1beta, IL-2, IL-6, and TNF-alpha secretion, and NKCC assessment.', 'Four hours after operation, the cells from patients in the ketamine group showed a significantly suppressed production of IL-6 (P < 0.01) compared with controls. The production of IL-2 did not change from that of the preoperation samples. TNF-alpha secretion was significantly elevated in the control group 4 h after operation (P < 0.05).'] Does low-dose ketamine affect immune responses in humans during the early postoperative period?