This study assessed the expression of complement receptor 1 (CR1), decay accelerating factor (DAF) and membrane inhibitor of reactive lysis (CD59) on the erythrocytes and glomerulus of diffuse proliferative glomerulonephritis (DPGN) of systemic lupus erythematosus (SLE) patients using flow cytometry and immunofluorescence techniques to elucidate their role in the pathogenesis of DPGN. Expression of CR1 on the erythrocytes and glomerulus of DPGN patients was reduced compared with expression in normal subjects. However, expression of DAF and CD59 was increased on both erythrocytes and glomerulus of DPGN patients, suggesting the generation of a protective response against complement-mediated injury.