In the present study we describe a method for the isolation of cell populations from human and rabbit atherosclerotic tissue, using monoclonal antibodies against cell surface antigen and magnetic microspheres. Atherosclerotic tissue was digested with proteolytic enzymes. The heterogeneous cell suspensions from human tissue were incubated with monoclonal antibodies: anti-Leu-4 (T lymphocytes), anti-Leu-M3 (macrophages) and anti-HLA-DR (HLA-DR expressing cells). The rabbit aortic cells were incubated with RAM11 (rabbit macrophages) antibody. The rosetting procedure was carried out by mixing antibody treated cells with magnetic monodisperse particles coated with a secondary antibody (goat anti-mouse IgG). Morphologically, homogeneous foam cell populations were isolated with anti-Leu-M3 and RAM11. From rabbit atherosclerotic aorta about 2 X 10(5) RAM11 positive cells were recovered/g tissue. The specificity was tested comparing with FACS analysis. A high degree of specificity was obtained while the FACS detected about 30% more cells than were isolated by immune depletion. The lipids of isolated macrophage derived foam cells from rabbit aorta were dominated by cholesterol ester (42%) and smaller amounts of unesterified cholesterol (17%) or triglycerides (3%). These experiments indicate that immunomagnetic fractionation of cells will be a useful method for studies of the composition and metabolism of different cell populations of atherosclerotic tissue.