Human studies suggest that free radicals and antioxidant enzymes can alter according to age, lifestyle, environment, and habits. Individuals having a marked circadian preference, that is, morning type or evening type, differ on a number of psychological, behavioral, and biological variables. The aim of this study was to determine whether chronotype impacts some parameters of oxidant and antioxidant status. For this purpose, glutathione peroxidase (GSH-P x), superoxide dismutase (SOD), and myeloperoxidase (MPO) activities and the levels of reduced glutathione (GSH) and malondialdehyde (MDA) were measured in 96 healthy volunteers (including 32 morning-type, 32 intermediate-type, and 32 evening-type individuals), aged between 21 and 26 years. There were no significant relationships between the chronotypes with regard to oxidant and antioxidant parameters. Our results indicated that the levels of GSH and MDA as well as the activities of GSH-P x, MPO, and SOD were not influenced by the individual circadian differences in our sample. These results were discussed using the theoretical concepts of age-related factors, and suggestions for further research presented. © 2012 Copyright Taylor and Francis Group, LLC.