For Immunological and immunopathological studies on lupus nephritis, kidneys from nine autopsied and one nephrectomized patients with systemic lupus erythematosus (SLE) were subjected to immunofluorescence(IF) and elution study. Six patients had diffuse proliferative lupus nephritis, showing granular or lumpy glomerular deposits by IF. Three had chronic renal failure with scanty glomerular deposits. One had no clinical renal disease but showed glomerular mesangial deposits. The serum level of antibodies to native(n)-DNA were slightly or moderately elevated in six patients. Hemolytic activity of serum complement(CH50) was markedly decreased in seven. Elution was performed as follows: the renal cortex was homogenized and washed repeatedly with cold saline, then the sediment containing glomeruli was disrupted by ultrasonication, and then suspended in 0.02 M glycine buffer, pH 2.8, in phosphate buffered saline for the control study. Antibodies to RNP were detected in six instances, and those to Sm in five. The hemagglutinating titers of antibodies to RNP and Sm in acid eluates were 8 to 128 times and 32 to 256 times higher than those in controls, respectively. However, when compared with the hemagglutinating titers in sera, specific enrichment of antibodies to RNP and Sm in acid eluates was less than 8 times. Three of ten acid eluates were demonstrated to contain antibodies to n-DNA which were determined by counterimmunoelectrophoresis(CIE). Two of these showed a positive precipitin reaction against denatured DNA. Minimum amounts of IgG producing positive reaction by CIE were measured in kidney eluates and sera obtained from the same patients. The ratio of the minimum concentrations of IgG in sera to those in eluates ranged between 33 and 125 with n-DNA system. Similarly, the ratio was between 33 and 62 with denatured DNA system. The results suggest that not just DNA immune complex but RNP and Sm immune complexes could be involved in the pathogenesis of lupus nephritis.