Adjuvant arthritis, induced by injections of Freund's complete adjuvant into the footpads of some rat strains, has been recognized as a useful animal model for many years. There has, however, been notable lack of success in reproducing this model in other species. We now describe the development of adjuvant arthritis in healthy strain mice approximately 2 months after injection of Freund's complete adjuvant. Although the clinical appearance of the mice and the joint histopathology closely resemble the adjuvant arthritis reported in the rat, we were unable to detect rheumatoid factor in sera from the affected animals. In parallel studies of T cell proliferation, affected animals responded to some mycobacterial antigens but not to the 65-kD heat shock protein of Mycobacterium tuberculosis, suggesting that some other epitope is important in the development of the disease.