BACKGROUND Coronary artery bypass surgery (CABG) with cardiopulmonary bypass (CPB) leads to elevated circulating plasma cytokines. In this prospective randomized study, the effect of an S-(+)-ketamine-based anaesthetic protocol on perioperative plasma cytokine levels was compared with standard anaesthesia with propofol and sufentanil during CPB. METHODS Patients undergoing elective on-pump CABG were randomly allocated to anaesthesia with sufentanil-propofol-midazolam (Sufentanil) or S-(+)-ketamine-propofol-midazolam (Ketamine). Blood samples were obtained before induction of anaesthesia (baseline) and also at 1, 6, and 24 h after aortic unclamping. Plasma levels of the interleukins (IL)-6, IL-8, IL-10, and tumour necrosis factor (TNF)-alpha were determined by enzyme-linked immunosorbent assay. RESULTS One hundred and twenty-eight patients were studied (Ketamine: n=60; Sufentanil: n=68). All measured cytokines increased during and after CPB. However, the increase in the pro-inflammatory cytokines IL-6 and IL-8 6 h after aortic unclamping was significantly lower in the Ketamine group compared with the Sufentanil group [mean (sd): IL-6 56.75 (46.28) pg ml⁻¹ (Ketamine) vs 172.64 (149.93) pg ml⁻¹ (Sufentanil), P<0.01; IL-8 7.74 (14.72) pg ml⁻¹ (Ketamine) vs 26.3 (47.12) pg ml⁻¹ (Sufentanil), P<0.01]. In contrast, the anti-inflammatory cytokine IL-10 showed higher levels 1 h after unclamping in the Ketamine group compared with the Sufentanil group [mean (sd): 69.59 (78.78) vs 24.63 (37.7) pg ml⁻¹, P<0.001]. CONCLUSION Our data demonstrate that S-(+)-ketamine possesses anti-inflammatory potential. Anaesthesia with S-(+)-ketamine may have beneficial effects in attenuating the CPB-induced systemic inflammatory response.