We retrospectively evaluated the morphologic change of 28 follow up biopsies from 24 cases of lupus nephritis according to the classification of the World Health Organization and determined the activity index (AI) and the chronicity index (CI). In the cases with biopsies repeated within 6 months, the AI decreased significantly from 6.7 +/- 1.3 to 3.5 +/- 0.8, while the CI showed no significant change. In cases which were rebiopsied after longer intervals, AI increased significantly from 3.2 +/- 0.7 to 7.5 +/- 1.2; the CI did not change significantly. When AI and CI changes in the cases biopsied again beyond 6 months were compared with respect to therapy, AI showed no significant difference in the methylprednisolone pulse therapy group but was significantly increased in the oral steroid therapy group. The CI tended to be increased in both groups, but not significantly. Steroid pulse therapy was effective in improving active lesions with a high AI. Steroid therapy for lupus nephritis prevented short-term progression of glomerulosclerosis and did not accelerate glomerulosclerosis.