OBJECTIVE: To compare patterns of Ro autoantigen recognition in primary Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). METHODS: Sera were tested by enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation for reactivity with recombinant human 60-kd and 52-kd Ro proteins. RESULTS: SLE and primary SS sera exhibited similar patterns of reactivity with the recombinant 52-kd protein. However, a greater proportion of sera from primary SS patients than from SLE patients did not react with recombinant 60-kd protein in ELISA yet precipitated its translation product in solution-phase assays. CONCLUSION: Disease state can influence recognition of the recombinant 60-kd Ro antigen.