During inflammation, myeloperoxidase (MPO) is released, for which its measurement in systemic circulation may be used as an index of leukocyte activation and oxidant stress. MPO levels correlate with angiographic evidence of coronary atherosclerosis and cardiovascular events in subjects with chest pain within the general population. We hypothesized that serum MPO levels are associated with adverse clinical outcomes in maintenance hemodialysis (MHD) patients.MPO levels were determined in serum samples from 356 MHD patients at the start of a 3-year cohort.Patients (46% women, 28% blacks, 54% with diabetes) were 54.6 +/- 14.6 (SD) years old and had undergone MHD for a median period of 26 months. Measured serum MPO level was 2,005 +/- 1,877 pmol/L (median, 1,444 pmol/L; interquartile range, 861 to 2,490 pmol/L). MHD patients with greater total body fat had greater MPO levels. MPO level had statistically significant (P < 0.01) and positive correlations with values for serum C-reactive protein (CRP; r = +0.15), interleukin 6 (IL-6; r = +0.23), tumor necrosis factor alpha (TNF-alpha; r = +0.21), and white blood cell count (r = +0.21). A death hazard ratio for each 1,000-pmol/L increase in serum MPO level was 1.14 (95% confidence interval [CI], 1.03 to 1.26; P = 0.01) after controlling for age, race (black), diabetes mellitus, dialysis vintage, Charlson comorbidity score, history of previous cardiovascular disease, blood hemoglobin level, and serum concentrations of albumin, CRP, IL-6, and TNF-alpha. After dividing MPO values into 3 equal groups (tertiles), the death hazard ratio of the highest tertile (versus the middle tertile) was 1.82 (95% CI, 1.07 to 3.10; P = 0.03).Serum MPO levels correlate with levels of markers of inflammation and prospective mortality risk in MHD patients.