The research is planned in order to analyse the physical and mental activities of ED workers on antioxidant system parameters. Enzyme activities of superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT), and levels of malondialdehyde (MDA) occurring as product of lipid peroxidation were examined in the blood samples taken prior to and after the shift of emergency department workers. Paired t-test was used to find out differences between pre- and post-shift values. An increase in MDA (1.77 +/- 0.33 versus 2.34 +/- 0.79 nmol/mL for pre-and post-shift; p < 0.001) and CAT (1.19 +/- 0.77 versus 4.33 +/- 1.35 K/mL for pre-and post-shift; p < 0.001) levels, and a decrease in SOD (30.34 +/- 8.11 versus 20.35 +/- 3.65 U/mg for pre-and post-shift; p < 0.001) and GPX (3.41 +/- 0.90 versus 1.37 +/- 0.38 U/mL for pre-and post-shift; p < 0.001) levels were found in comparison with the measurement levels of the blood samples. The results were found to be statistically signifi cant. Oxygen free radicals play an important role in some degenerative and mental diseases. Accordingly, physicians and the other emergency department workers should be trained regarding the stress in the conditions they work in. Copyright (C) 2010 John Wiley & Sons, Ltd.