Using previously developed spectro-photonmetrical method (Bioorg. Khim. 2009. V. 35. pp. 629-639), a significant increase of myeloperoxidase (MPO) activity was found in blood plasma of patients with type 2 diabetes mellitus (DM2) without of cardiovascular complications, as well as with ischemic heart disease (IHD). Plasma MPO concentration measured by an enzyme-linked immunosorbent assay was significantly higher only in blood plasma of patient with DM2 and IHD. A direct and significant correlation between MPO activity and MPO concentration was observed only in blood plasma samples from healthy donors. Increased MPO activity did not correlate with MPO concentration in blood plasma of patients with DM2 and DM2 with IHD. Taken together, these results highlight the necessity for studying of the MPO role in the development of pathological processes to determine both the amount of enzyme and its peroxidase activity in the blood. The proposed approach gives comprehensive information about the relationship between MPO activity and MPO concentration in patient blood. Since the high concentration of MPO is a diagnostically significant parameter in the prediction of endothelial dysfunction and cardiovascular disease development, the obtained results evidence the contribution of MPO-dependent reactions in cardiovascular complications associated with diabetes. MPO activity may serve as an additional diagnostic criterion for determination of risk of IHD in DM patients.