Objective: We aimed to investigate the short-term effect of laparoscopic surgery on serum thiol-disulfide homeostasis levels as a marker of oxidant stress of surgical trauma in elective laparoscopic cholecystectomy patients. Materials and Methods: Venous blood samples were collected, and levels of native thiols, total thiols, and disulfides were determined with a novel automated assay. Total antioxidant capacity (measured as the ferric-reducing ability of plasma) and serum ischemia modified albumin, expressed as absorbance units assayed by the albumin cobalt binding test, were determined. Results: The major findings of the present study were that native thiol (28345 versus 241 +/- 61mol/L), total thiol (313 +/- 49 versus 263 +/- 67mol/L), and disulfide (14.9 +/- 4.6 versus 11.0 +/- 6.1mol/L) levels were decreased significantly during operation and although they increased, they did not return to preoperation levels 24 hours after laparoscopic surgery compared to the levels at baseline. Disulfide/native thiol and disulfide/total thiol levels did not change during laparoscopic surgery. Conclusions: The decrease in plasma level of native and total thiol groups suggests impairment of the antioxidant capacity of plasma; however, the delicate balance between the different redox forms of thiols was maintained during surgery.