The pattern of changes in the neutrophil myeloperoxidase (MPO) levels in various atherosclerotic conditions was analyzed by assessing the mean myeloperoxidase index (MPXI), which is calculated during the routine complete blood count (CBC) performed using the flow-cytochemistry blood autoanalyzer ADVIA120/2120 (Siemens), and plasma MPO concentrations. MPXI values of ischemic heart disease (IHD) patients did not differ from those of healthy volunteers. However, MPXI values of IHD patients with arteriosclerosis obliterans (ASO) (-6.1 ± 1.8) were significantly lower than those of IHD patients without ASO (0.8 ± 0.5). In contrast, the MPO values in IHD patients with ASO were significantly elevated. In subjects without IHD, while the MPXI values in mild cases of ASO (Fontaine's stages I/II, 3.4 ± 0.8) were significantly higher than those of healthy volunteers (0.4 ± 0.4), the values of those with severe ASO (stages III/IV, 0.3 ± 0.8) were significantly lower than those of mild cases. However, when ASO patients developed IHD, the MPXI values dramatically decreased (stages I/II, -7.3 ± 1.9; stages III/IV, -5.2 ± 1.6). These results indicate that MPXI is elevated in mild, but not in severe, ASO cases, and that MPXI decreases dramatically when ASO patients develop IHD. MPXI may constitute an informative independent biomarker for diagnosis and follow-up of IHD complicated by ASO.