The performances of the OXY-SCORE, a summary index of oxidative stress, and of its individual components (plasma malondialdehyde (MDA), oxidized and reduced glutathione, individual antioxidant capacity, alpha- and gamma-tocopherol and urinary isoprostanes) were assessed in 47 patients undergoing coronary surgery, randomly assigned to cardiopulmonary bypass (CPB) or off-pump procedure (OPCAB) associated with less oxidative stress. The ability of the OXY-SCORE to classify correctly the patients was high (area under the ROC curve 0.90). Only free MDA showed a similar performance, but it was insensitive to the minor variations of the oxidative balance in the OPCAB group.