BACKGROUND: As immune mediators, cytokines are thought to regulate many biological functions. Changes in cytokine response were found in stressful conditions including surgery. Our aim was to study the effects of oral clonidine premedication on the proinflammatory and antiinflammatory cytokines in patients undergoing spinal fusion. METHODS: Thirty patients (ASA I and II) were selected and randomly assigned to one of the three groups. Group 1, 2, and 3 received no premedication, clonidine 0.15 mg and 0.3 mg orally, respectively. Blood concentrations of proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta), IL-6, and antiinflammatory cytokines IL-10, IL-13 were determined as following intervals: before induction, immediate, 1 h, 3 h and 5 h after incision. For cytokines assay, commercially available ELISA kits were used. RESULTS: Compared to baseline values, TNF-alpha , IL-6 and IL-10 concnetrations at 3 h and 5 h after incision increased significantly in all the individual groups. IL-1beta increased significantly at 3 h and 5 h after incision in group 1 and 3, and at immediate, 1 h and 3 h after incision in group 2. At the same times sampled, TNF-alpha, IL-1beta, IL-6, IL-13 concentrations were not statistically different among three groups. However, IL-10 concentration increased significantly at 5 h after incision in group 2 and 3 compared to group 1. In addition, IL-10 level at 5 h after incision in group 2 was significantly different from group 3. CONCLUSIONS: Oral clonidine premedication increased release of antiinflammatory cytokine IL-10 significantly during spinal fusion surgery.