22 nephrectomy specimens of renal allografts in chronic rejection after periods between 3 and 96 months, were studied immunohistologically. Various cell types in the arterial wall were characterized with antibodies specific against different cells of the mononuclear phagocyte system, against smooth muscle cells, and against differentiating lymphoid cells. In addition, the metabolism of lipoproteins was investigated using appropriate antibodies against several apolipoproteins. Subendothelial plaques of foam cells were found to consist of macrophages in foamy transformation. At the stage of intimal fibrosis the smooth muscle cells are more prominent. Lymphatic infiltration consists almost exclusively of T-lymphocytes. Apolipoprotein analysis reveals deposits of Apo A1, A2 and B1, most of them extracellular. According to these results, it is not only immunologic factors that are involved in arterial wall reactions during chronic transplant arteriopathy, but disorders of the lipoprotein metabolism--probably due to endothelial dysfunction--are also playing an important role like in atherosclerosis.