The oxidative modification of low-density lipoprotein (LDL) is thought to contribute to atherogenesis, and there is evidence that oxidants derived from myeloperoxidase (MPO) contribute to such oxidative damage. Using human iliac arteries we investigated the relationship between lesion stage indicated by the intima-to-media (I/M) ratio and the presence of apolipoprotein B-100 (apoB, a marker for LDL), MPO, and hypochlorite (HOCl)-oxidized proteins identified by immunohistochemistry in the intima, media, and adventitia. More staining for apoB, MPO, and HOCl-oxidized proteins was observed in diseased than healthy vessels. Diseased segments also stained more for the three parameters than healthy segments in the same diseased vessel, highlighting the variability that can occur within a single cross-section of a vessel. However, significant positive correlation between I/M ratio and positive staining for apoB, MPO, and HOCl-oxidized proteins in different segments of individual arteries were apparent in segments with an I/M ratio of > 1.8. Also, the overall extent of intimal staining for apoB, MPO, and HOCl-oxidized proteins increased with increasing I/M ratio. In addition, the extent of apoB staining was greater and appeared at comparatively lower I/M ratios than that of MPO and HOCl-oxidized proteins. Our results support a contribution to atherogenesis of all three parameters assessed, although MPO and HOCl-oxidized proteins appear to participate in the disease process at a later stage than apoB.