The presence of desmin, regarded as a marker of myogenic cells, in glomerular epithelial cells (GECs) of the kidney was studied in four strains of rat (SHR, Lewis, Fischer 344, WKA) by immunofluorescence microscopy and immunoelectron microscopy. Some of the GECs were stained with both monoclonal and polyclonal anti-desmin antibodies. The frequency of desmin-positive cells among GECs varied between glomeruli in each of the strains and also differed between the four strains. Most GECs in WKA rats contained desmin, whereas few did so in SHR rats. Lewis and Fischer 344 rats showed amounts of GEC desmin staining intermediate between those of SHR and WKA rats. In every strain, desmin-specific immunofluorescence in GECs increased with aging. In aminonucleoside nephrosis, GECs showed extremely enhanced desmin staining in parallel with urinary protein excretion. This heterogeneous distribution and changes observed for desmin were not shown for vimentin. On the basis of the above findings, the correlation between the presence of desmin in GECs and glomerular epithelial damage is discussed.