The sequential histologic changes in a bovine serum albumin (BSA)-induced model of chronic arthritis are described. The deposition of antigen in cartilage appears responsible for the localization of the chronic phase of the lesion, which predominates in synovium contiguous with the meniscus and periarticular ligaments. Theoretically, removal of antigen or immune complexes could play a key role in therapy of immune-mediated arthritis.