The aim of this study was to investigate how myeloperoxidase (MPO) G-463A gene polymorphism and enzyme levels varied among patients with chronic lymphocytic leukemia (CLL) and multiple myeloma (MM) and to find the relationship between the MPO gene, enzyme levels, and clinical parameters. We studied the sera from 40 healthy volunteers, patients with CLL (n = 34) and MM (n = 28). In subjects with homozygote GG genotype, MPO levels were higher in the patients with both CLL and MM than in the control group. This difference was statistically significant in patients with CLL. In conclusion, homozygote GG genotype is found to be associated with an increasing amount of serum MPO. In accordance with the results of the study, we assess that the increase in the MPO enzyme level in the patient groups with CLL and MM generated bactericidal effects as well as the increased formation of ROP, thus setting off a pro-cell death pathway and playing a role on the pathogenesis of lymphoproliferative malignancies through this mechanism.