Glomerular epithelial cells (GECs) have been considered as post-mitotic cells. In order to establish the stage when GECs stop dividing, the expression of proliferating cell nuclear antigen (PCNA/cyclin) in GECs during glomerulogenesis in human kidneys was studied by the streptavidin-biotin staining technique with monoclonal antibodies. Antibody specific for PCNA/cyclin reacted with almost all the cell nuclei of nephrogenic vesicles, as well as those of S-shaped bodies, the cells of which in the lower limb are progenitors of GECs. However, this reaction was markedly reduced in GECs at the capillary loop stage and entirely disappeared at the maturational stage. In contrast to the expression of PCNA/cyclin, vimentin-specific antibody did not react with nephrogenic vesicles and the lower limb of S-shaped bodies, whereas vimentin was ubiquitously expressed in the GECs at the capillary loop stage, as well as at the maturational stage. Furthermore, these two antigens were not co-expressed in the same glomerulus during glomerulogenesis, as revealed by analysis of serial sections. These results lead to the conclusion that expression of PCNA/cyclin and vimentin during glomerulogenesis is fairly stage-dependent, and GECs rapidly lose their mitotic activity at the capillary loop stage.