The role of autoimmunity to type II collagen in the arthritis of systemic lupus erythematosus (SLE) has been assessed by ELISA and by Western blotting cyanogen bromide cleavage fragments separated on SDS-PAGE. The results show that antibodies to both native and heat-denatured collagen are quite common in SLE when measured by ELISA. Of particular interest is the demonstration of an association between antibodies to the CB 11 peptide and deforming arthritis in SLE. This is the arthritogenic peptide in murine models of collagen II-induced autoimmune arthritis and the results presented here suggest a potential pathogenetic role in the deforming arthritis of SLE for this specific subset of antibodies to type II collagen.