The purpose of this research was to evaluate the plasma protein carbonyl groups (PC) in 81 trained subjects (TS) who practiced regular, non professional physical activity. They were divided into three groups according to the type of sport they practiced (endurance, mixed or power). On fasting venous blood we examined the PC groups employing an enzyme-linked immunosorbent assay (ELISA) kit, in which 2,4-dinitrophenyl-hydrazine reacts with the PC forming a stable hydrazone product. In the whole group of TS a significant decrease in PC was present, in comparison with sedentary controls (SC). Dividing TS into groups, we observed a decreased PC concentration in those practicing endurance and mixed sports, but not in those practicing power sports. There was no difference between men and women for PC either in SC or in TS; male TS had a PC concentration significantly lower than male SC. Our data show that body proteins are more protected against oxidative stress in subjects who practice endurance and mixed sports. These results give further support to the promotion of regular physical activity including aerobic exercise.