The lupus-prone (NZB x NZW)F1 female mice (NZB/W) develop an autoimmune disease characterized by production of autoAb and fatal glomerulonephritis. Since it has been previously shown that total lymphoid irradiation has a beneficial effect in this model, we have analyzed whether early thymic irradiation (ETI) could improve the course of the lupus-like syndrome in these mice. NZB/W mice received thymic irradiation (4500 rads) beginning at 10 weeks of age, prior to the onset of autoimmune manifestations. Then, they were evaluated for survival, renal histology, and serological markers of autoimmunity, in comparison to nonirradiated NZB/W females. The treatment with ETI improved nephritis and survival in NZB/W mice: 50% mortality was observed at 12 months in irradiated mice and at 9 months in untreated mice. This improved survival could not be attributed to a reduction in the titers of anti-dsDNA Ab nor in the levels of total immune complexes which were essentially identical in both groups. By contrast, this improvement was related to a selective normalization in the serum levels of IgG3 and gp70-anti-gp70 immune complexes (gp70IC) in ETI NZB/W female mice as compared to that seen in nonirradiated NZB/W females. These data show the therapeutical effect of ETI and support the pathogenic role of IgG3 and gp70IC in the development of glomerulonephritis in NZB/W mice.