Objective: To measure the amount of lipid peroxidation and erythrocyte antioxidation in patients undergoing laparoscopic and open cholecystectomy and healthy controls. Design: Non-randomised study. Setting: University hospital, Istanbul. Subjects: 31 patients, of whom 14 underwent open and 17 laparoscopic cholecystectomy, and 15 healthy controls. Interventions: Heparinised blood samples were taken from the patients immediately after operation and from the healthy controls. Main outcome measures: Lipid peroxidation index as expressed by thiobarbituric-acid-reactive substances (TBARS) and components of the erythrocyte antioxidant defence system, namely reduced glutathione, reduced glutathione peroxidase (glutathione-Px) and CuZn superoxide dismutase (CuZn SOD) in patients undergoing open or laparoscopic cholecystectomy and healthy controls. Results: All 4 variables were significantly higher in the cholecystectomy groups than in controls (p < 0.001), and laparoscopic cholecystectomy caused significantly less oxidative stress than the open operation (p < 0.001). Conclusion: Both types of cholecystectomy cause oxidative stress and lead to an adaptive antioxidant response in the body. However; both oxidative stress and the antioxidant response are more pronounced after traditional open cholecystectomy. [ABSTRACT FROM AUTHOR]