Abstract： In this study,the expression and distribution of HLA-DR antigen in transplanted kidneys were tested and the possible diagnostic value of HLA-DR expression in rejection was evaluated.Forty kidney recipients were enrolled in this study.The results showed that there were both increased expression and altered distribution of HLA-DR antigen in the transplanted kidneys.The expression of HLA-DR antigen was in three fashions:diffusely increased expression,segmentally increased expression and basically normal expression.There were also strong positive and weak positive expression in degree.An markedly increased and sustained expression of HLA-DR antigen were found in irreversible rejection and acute rejection.While in chronic rejection,further studies were needed to evaluate the expression.