Abstract: Biodegradable, protein microspheres for in vivo release of a biologically active agent, as well as agricultural and environmental applications. The microspheres can be administered orally, intravenously, or subcutaneously for subsequent release. By selecting particular size ranges and the specific protein used to form the microsphere, it is possible to target the microspheres to a cell types such as macrophages, or to effect localized absorption of the microspheres to regions such as the mucosal membranes of the mouth, gastrointestinal tract, or urogenital areas. Larger forms of the microspheres can also be made using standard techniques of the desirable degradation properties.