Antibodies to dsDNA, tested with circular DNA in the Farr assay, are specific for systemic lupus erythematosus. A longitudinal study showed a clear relation between the clinical state, the anti-dsDNA titer (expressed in units), and the C1q and C3 levels: when anti-dsDNA levels remained high, no exacerbations were observed. A sharp drop in anti-dsDNA, usually preceded by a rise, was related to a serious exacerbation. Only during the exacerbation when both C1q and C3 were very low was renal involvement seen.