Marked fluctuations in the levels of a common DNA-antibody idiotype, PR4-Id have been found on IgM and IgA antibodies in particular and to a lesser extent on IgG in serial bleeds of 14 lupus patients. Few clear cut examples were found of the PR4-Id levels reflecting disease activity. However, the idiotype expression was not simply related to total immunoglobulin levels and the controlling mechanisms of idiotype expression on different isotypes remain a matter of conjecture.