A new magnetic microsphere carrier has been formulated that may localize drugs by both biochemical and physical means. The microspheres, prepared from the polysaccharide chitosan, are designed to bind to anionic glycosaminoglycan receptors on the surface of capillary endothelial cells. The microspheres were formulated to have a controlled cationic character and had a mean diameter of 0.70 micron and a magnetite content of 16% (w/w). Formation of complexes between chitosan and heparin and between the microspheres and heparin has been demonstrated. Heparin served as a model glycosaminoglycan. The chitosan:heparin complex ratio was found to be 1:1 based on charge and was formed between ammonium ions on the chitosan and SO3- groups on heparin. Neutralization of the charge on the microspheres prevented their complexation with heparin. The rationale for the use of the delivery system and its potential limitation are discussed.