Aim Evaluating the redox potential of white blood cells (WBC) in acute coronary syndrome (ACS) depending on the presence or absence of type 2 diabetes mellitus (DM2).Material and methods The study included 100 men and women aged 35 to 65 years who were managed for ACS at the Primary Vascular Department (PVD) of the Vladivostok Clinical Hospital #1. The control group consisted of 30 healthy volunteers matched with ACS patients in major anthropometric characteristics. Examinations were performed according to clinical recommendations. Blood was withdrawn for measuring cell activity of enzymes (superoxide dismutase, SOD; succinate dehydrogenase, SDH; and glutathione reductase, GR) and serum concentration of malonic dialdehyde (MDA). Based on the ACS type, all patients were divided into 3 main ACS groups, and then the groups were subdivided into subgroups based on the presence of DM2.Results Development of ACS was associated with changes in WBC redox potential. These changes were characterized by a significant decrease in SDH activity in all ACS patients, irrespective of their ACS type, and a moderate decease in GR in patients with myocardial infarction compared to patients with unstable angina and healthy volunteers. At the same time, the SOD activity and MDA concentration were practically unchanged compared to the control group. There were practically no significant differences in the enzyme activities between the ACS subgroups with or without DM2.Conclusion The WBC activities of SDH and GR on day 1 of ACS can be considered as the indicators for early diagnosis of mitochondrial dysfunction resulting from the cardiovascular catastrophe as well as the markers for impaired primary cell defense. MDA and SOD values are not informative for determining the intensity of oxidative stress and further damage of the antioxidant system.