Antibodies to dsDNA of the IgG-class show a strong association with disease activity in the course of systemic lupus erythematosus (SLE). Of 22 patients with low dsDNA-levels only one had an exacerbation. In 8 patients a rise of IgG-dsDNA antibodies to high levels occurred, followed by an exacerbation in 7 of them. In 6 of these 7 patients the IgG-dsDNA antibodies had a prognostic value by rising into high ranges 2-12 weeks before the exacerbation. IgG-ssDNA antibodies showed only a weak association to the clinical course. IgM antibodies to dsDNA as well as to ssDNA did not correlate with the clinical activity at all.