A historical review and the present author's study on diabetic nephropathy have been presented.Three characteristic lesions in KW‐lesion, namely nodular, exudative and doughnut lesion may all be regarded as to be caused by severe circulatory disturbance occurring in intraglomerular branches of the afferent artery. This circulatory disturbance is considered to be brought about by sudden spasm of the peripheral portion of the afferent branches. The diffuse form of Bell may be regarded as to be a slighter type without severe mesangiolysis. Arteriolar hyalinosis and arteriosclerosis and/or atherosclerosis may be caused by intraglomerular circulatory disturbances. The most important problem in diabetic nephropathy, including KW‐lesion and Bell's diffuse form, is to elucidate the mechanism leading to the occurrence of spasm of the peripheral portion of intraglomerular afferent branches. Becker4found fixation of antiactomyosin‐antibody in the mesangial tissue by the immunofluorescent method. Many studies along this line have been made, but none are adequate in fully explaining the mechanism inv