The authors have recently shown that antibodies with anti-idiotype (Id) specificity to pathogenic Ids of lupus nephritis may occasionally occur in several intravenous immune globulin (IVIG) preparations because they are present in healthy donors and the healthy relatives of SLE patients. In the present study, the authors purified these anti-Ids and treated two SLE patients with nephritis in parallel with conventional high-dose IVIG management with a commercial preparation (IVIG 6) in three controls for two months. Because pathogenic Ids of anti-DNA molecules, such as both 8.12 and F4 Ids, show a cationic mobility in isoelectric focusing, a commercial preparation of IVIG (11) was absorbed on a Sepharose column coupled with DC-305-39 myeloma protein, namely an 8.12+ and F4+ cationic IgG. Infusion of the eluate (EL-11) induced a prompt resolution of proteinuria levels and an evident decrease of serum levels of anti-DNA antibodies in both patients, whereas in the three controls, proteinuria and anti-DNA antibodies were scarcely reduced. In addition, plasma levels of interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha were also significantly influenced by both treatments. The mean values of both cytokines increased significantly after 1 h and then progressively declined over the next 48 h. It was of interest, however, that the increased TNF-alpha in the two EL-11-treated patients was significantly lower than in the three controls. The data suggest that reduction of active lupus nephritis by enriched specific anti-Id molecules is the result of two (or perhaps more) mechanisms: suppression of pathogenic idiotypes at the cellular level and improvement in the mesangium of the secretion of anti-inflammatory cytokines, such as IL-6, whose defective function is related to the autoimmune disorder.