Both hypercholesterolemia and vascular injury have been reported to induce macrophage infiltration, but their combined effect and the mechanism by which hypercholesterolemia enhances the infiltration remain to be clarified in vivo. To evaluate the effect of hypercholesterolemia on macrophage infiltration after vascular injury, the iliac arteries of hypercholesterolemic (HC) and normocholesterolemic (NC) rabbits were examined 2 h, 1 day, 3 days, 7 days, and 14 days after balloon injury using immunohistochemical staining for macrophages, intercellular adhesion molecule (ICAM)-1, and vascular cell adhesion molecule (VCAM)-1. Nuclear factor kappa-B (NF-κB) activation was also evaluated in fresh frozen iliac arteries using the electrophoretic mobility shift assay method. The fundamental difference between HC and NC was the amount of macrophage infiltration seen in HC from 7 days after balloon injury. Two out of 4 HC iliac arteries on the 7th day, and 3 out of 4 HC iliac arteries on the 14th day were positively stained with ICAM-1 in regenerated endothelium and neointima, whereas there were no positively stained NC iliac arteries. Neither HC nor NC tissues showed positive staining with VCAM-1. NF-κB was activated in HC 7 and 14 days after balloon injury, but not in NC. In conclusion, in vivo hypercholesterolemia induces macrophage infiltration after balloon injury and it is mediated by increased NF-κB activation promoting ICAM-1 expression. (Jpn Circ J 2001; 65: 117 - 122)