Although the pathology of discoid lupus erythematosus is well documented the causative agents are not known. Here, we report the identity of the target antigen of an autoantibody present in high titre in the serum of a patient with discoid lupus erythematosus. We have demonstrated that the antigen is enolase; first, because it has properties consistent with this glycolytic enzyme (47,000 MW, cytosolic localization and ubiquitous tissue distribution). Secondly, limited amino acid sequence determination after trypsin digestion shows identity with alpha-enolase. Finally, the autoimmune serum immunoblots rabbit and yeast enolase and predominantly one isoelectric form of enolase (PI approximately 6.1). These results indicate that the reactive autoepitopes are highly conserved from man to yeast. The results also suggest that the autoantibodies are most reactive to the alpha-isoform of enolase, although it is possible that they may also be reactive with gamma-enolase, and have least reactivity to beta-enolase. The anti-enolase autoantibodies belong to the immunoglobulin G1 (IgG1) isotype. This is the first report of IgG1 autoantibodies to evolutionarily conserved autoepitopes of enolase in the serum of a patient with discoid lupus erythematosus. Previous reports of autoantibodies to enolase have suggested associations with autoimmune polyglandular syndrome type I and cancer-associated retinopathy. This report and an earlier report of what is likely to be enolase autoantibodies in two patients without systemic disease suggest that enolase autoantibodies have a broad association and are not restricted to any particular disease.