Collagen-induced arthritis can be transferred from immunized arthritic rats to unimmunized recipients by intravenous injection of an immunoglobulin concentrate of sera. This study identifies antibodies in the transfer concentrate which localize to the articular surface of cartilage in joints of recipients. Immunoglobulin can also be demonstrated in the same location in arthritic joints from rats after immunization. Antibody capable of transferring arthritis is present in donor rats over a period of at least 3 weeks and can be absorbed using homologous type II collagen. In addition, anti-type II collagen antibodies can be eluted from arthritic joints of rats with early disease.