Previous evidence suggests that malignant tumors cause an oxidative burden to human antioxidative defense systems. We followed the plasma total radical-trapping antioxidant parameters (TRAP) and their main antioxidant components (alpha-tocopherol, uric acid, protein sulfhydryl groups, and unidentified antioxidant proportions) in 13 lung cancer patients and 7 control patients scheduled for thoracotomy. Plasma samples were collected 9 times during a 5 month follow-up period in the cancer patients. The objective of the study was to evaluate the effects of surgical removal of lung cancer on human plasma total antioxidant capacity. A significant reduction of plasma TRAP (period effect of ANOVA, p = 0.0006) and its components appeared in both groups during the first postoperative day. This decrease was due to reduction of ascorbate (p = 0.002) alpha-tocopherol (p = 0.0001) and urate (p = 0.05) concentrations. At 3 and 5 months after the surgical removal of the tumor there was an augmentation in plasma TRAP concentrations (p = 0.02, 3 months; p = 0.07, 5 months). This was mainly due to the increases in plasma yet as unidentified antioxidant components (UNID) and protein SH-groups. The data indicates that, first, thoracotomy itself causes a reduction in plasma TRAP during the early hours after operation, and secondly surgical removal of lung cancer increases plasma TRAP concentrations compared to the baseline values possibly reflecting the relief of oxidative stress caused by malignant tumors.