Interendothelial and subendothelial monocytes/macrophages are extremely rare in normal rabbit aortas compared with humans and swine, as has been shown by the present study and previous investigations of surface preparations. Light microscopy was used to study the development of immune complex-induced hematogenic macrophage infiltrations in 26 rabbits from the 4th to the 28th day after the last antigen administration. Of particular interest was the intensity, localization and duration of the hematogenic cell infiltrates with a view to establishing the role of immunological stimuli for subendothelial monocyte and lymphocyte accumulation. It was found that immune complex-induced hematogenic macrophage infiltrates are very short-lived and disappear after 20-28 days following immune complex deposition. They concentrate in the ostium regions of the thoracic and abdominal aorta and are subject to flow dynamics similar to those of cholesterol-induced sudanophile lipid deposition. Subendothelial macrophage infiltrates increase the permeability of the aorta for low-molecular but not for macromolecular plasma particles, do not affect the endothelial silver line picture and do not lead to lipid accumulation.