Experimental allergic encephalomyelitis (EAE) is an inflammatory disease of the central nervous system (CNS). Among the leukocytes which infiltrate the CNS during EAE, numerous macrophages are present. These macrophages are thought to play a crucial role in the generation of tissue damage and attendant neurological deficits. The mechanism by which the macrophages migrate across the blood-brain barrier is not yet clear. Membrane proteins involved in macrophage adherence to the endothelium include the CD11b/CD18 integrin, also known as the type 3 complement receptor (CR3). In this study we show that two monoclonal antibodies (mAb) ED7 and ED8 are directed against rat CR3. In addition, these mAb reduce recruitment of myelomonocytic cells towards thioglycollate induced peritonitis by 15-33%. This indicates that both ED7 and ED8 interfere with an epitope on CR3, which is involved in recruitment of phagocytes towards inflammatory lesions. Intravenous injection of ED7 and ED8 suppressed clinical signs of EAE. MRC OX-42, which also recognizes CR3, did not reduce thioglycollate-induced phagocyte recruitment into the peritoneum, and had no effect on EAE. These findings suggest that CR3 plays a role in the recruitment of macrophages towards the inflamed CNS of EAE animals, and confirm the role of macrophages in the generation of clinical signs of EAE. Involvement of CR3 in other phagocyte immune functions during EAE is discussed.