Rabbits immunized with ultraviolet-irradiated DNA (UV-DNA) produced high titers of serum antibody. This experimental model was studied to determine if injection of antigen (UV-DNA) intravenously into immunized animals would induce glomerulonephritis and proteinuria. Proteinuria was observed several days after the start of daily intravenous injections into immunized animals and was sustained as long as injections were continued, but fell to normal values after stopping antigen administration. The kidneys showed glomerulitis sometimes associated with focal proliferative lesions, and immunofluorescence showed rabbit Ig and C3 in glomeruli. By electron microscopy, electron-dense subendothelial deposits were seen. Sucrose density gradient analyses of sera immediately after antigen injections suggested the presence of immune complexes of DNA and antibody since both heavy sedimenting and 7S Ig were detected. After digestion with deoxyribonuclease rabbit Ig could be found only in the 7S sedimenting fractions. Intravenous injection of UV-DNA into normal, nonimmune animals did not produce heavy sedimenting Ig or abnormal sedimentation patterns. These studies with an experimental model might provide insight into pathogenetic mechanisms operating in systemic lupus erythematosus where the importance of DNA-anti-DNA immune complexes have been documented. The studies suggested that gradual accumulation of DNA immune complexes in glomeruli might be one mechanism causing renal functional abnormalities.