The magnitude of the tissue damage from surgery impacts the trauma response. This response is proportional to the severity of surgical stress. Systemic cytokines are recognized as markers of postoperative tissue trauma. Microendoscopic discectomy (MED) recently has become popular for treating lumbar disc herniations, and is associated with favorable clinical outcomes compared with open discectomy (OD). This study postulates that MED is a less traumatic procedure, and therefore has a lower surgical stress response compared to OD. In this study, a quantitative comparison of the overall effects of surgical trauma resulting from MED and OD was performed through analyzing patient systemic cytokines response. From April, 2002 to June, 2003, 22 consecutive patients who had symptomatic lumbar disc herniations were prospectively randomized to undergo either intracanalicular MED (N=10) or OD (N=12). In this study, the Vertebroscope System (Zeppelin, Pullach, Germany) was used to perform the endoscopic discectomy procedure in all MED patients. Serum levels of tumor necrosis factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta), Interleukin-6 (IL-6), and Interleukin-8 (IL-8) were measured before surgery and at 1, 2, 4, 8 and 24h after surgery using an enzyme-linked immunosorbent assay. Serum C-reactive protein (CRP) was measured at the same time interval. The results showed the MED patients had shorter postoperative hospital stay (mean, 3.57+/-0.98 vs. 5.92+/-2.39 days, p=0.025) and less intraoperative blood loss (mean, 87.5+/-69.4 vs. 190+/-115 ml, p=0.042). The operating length, including the set-up time, was longer in the MED group (mean, 109+/-35.9 vs. 72.1+/-17.8 min, p=0.01). The mean size of skin incision made for the MED patients was 1.86+/-0.13 cm (range 1.7-2.0 cm); and 6.3+/-0.98 cm for the OD patients (range 5.5-8 cm), p=0.001. The patients' pain severity of the involved limbs on 10-point Visual Analog Scale before operation in MED group was 7.5+/-0.3 (range 6-9) and 8+/-0.2 (range 7-9) in OD group, p=0.17; and after surgery, 1.5+/-0.2 (range 1-2) in MED group and 1.4+/-0.1 (range 1-3) in OD group, p=0.91. CRP levels peaked at 24h in both groups, and OD patients displayed a significantly greater postoperative rise in serum CRP (mean, 27.78+/-15.02 vs. 13.84+/-6.25mg/l, p=0.026). Concentrations of TNF-alpha, IL-1beta, and IL-8 were detected only sporadically. Serum IL-6 increased less significantly following MED than after OD. In the MED group, IL-6 level peaked 8h after surgery, with the response statistically less than in the open group (mean, 6.27+/-5.96 vs. 17.18+/-11.60 pg/ml, p=0.025). A statistically significant correlation was identified between IL-6 and CRP values (r=0.79). Using the modified MacNab criteria, the clinical outcomes were 90% satisfactory (9/10) in MED patients and 91.6% satisfactory (11/12) in OD patients at a mean 18.9 months (range 10-25) follow-up. Based on the current data, surgical trauma, as reflected by systemic IL-6 and CRP response, was significantly less following MED than following OD. The difference in the systemic cytokine response may support that the MED procedure is less traumatic. Moreover, our MED patients had achieved satisfactory clinical outcomes as the OD patients at a mean 18.9 months follow-up after surgery.