Accidental and operative trauma are able to induce a systemic reaction of the organism characterized by fever, leukocytosis, catabolism, and an activation of the coagulation system. Interleukin-6 (IL-6) has been found to be an important mediator of this acute-phase response. In this study the influence of elective craniotomy on IL-6 plasma levels was evaluated. Blood samples were obtained from 20 patients undergoing elective craniotomy for vascular or tumorous diseases of the brain. IL-6 increased significantly (p < 0.05) from the pre-operative (0(0-5.4) pg/ml) to the intraoperative (180 min after beginning of surgery) time-point (10.6 (0-18.5) pg/ml). The maximum was reached on the first postoperative morning (13.9(4.3-45.0) pg/ml). Interleukin-10 (IL-10) is an anti-inflammatory cytokine which suppresses IL-6 synthesis in vitro in various cell lines. IL-10 plasma concentrations showed no alterations throughout the study period. Epinephrine plasma concentrations increased significantly from pre-operative values (15 (0-74) pg/ml) to the postoperative time-point (57(9-459) pg/ml). A 4.5-fold increase (p < 0.05) of norepinephrine plasma concentrations was found when comparing the data obtained 60 min after beginning of surgery with the data of the first postoperative morning. In monocytes, which are a major source of plasma IL-6, an elevation of intracellular cAMP stimulates the IL-6 synthesis. The postoperative maximum of IL-6 in plasma could be due to a release of catecholamines. In conclusion this study demonstrated an elevation of IL-6 plasma concentrations during and after elective craniotomy. Increased plasma catecholamine concentrations as well as a damage in the blood-brain barrier due to the surgical trauma with a spill-over of IL-6 from brain tissue into plasma could have contributed to this result.