Recent studies have shown that anti-DNA and anticardiolipin antibodies in patients with SLE may cross-react. Using an ELISA for determination of these antibodies, a strong association between IgG anti-denatured DNA and IgG anticardiolipin antibodies was found. Eight sera samples with the highest levels of both antibodies were selected to determine the possibility of a cross-reaction. The levels of anticardiolipin were not affected by denatured DNA in concentrations adequate to inhibit the anti-DNA binding. These data did not confirm previous studies using monoclonal antibodies showing cross reactivity between the two groups of antibodies. Nevertheless, a population of antibodies that may cross-reacts, in some special cases, cannot be ruled out.