We purified the constitutive 73-kDa heat-shock protein (HSP73) from the bovine brain, and produced a specific antibody against the protein in a rabbit. On immunoblotting, the antibody cross reacted only with a protein band with a molecular mass of 73 kDa in a crude extract from normal rat kidneys, which was regarded as rat renal HSP73. The intrarenal immunohistochemical distribution of HSP73 was examined by using this antibody, on both normal rat kidneys and kidneys with puromycin aminonucleoside nephrosis. HSP73 was predominantly present in epithelial cells of the glomeruli and the tubules. In normal kidneys, HSP73 was generally localized in both the cytoplasm and the nucleus of these epithelial cells, except for proximal tubular epithelial cells. On the other hand, in kidneys with puromycin aminonucleoside nephrosis, HSP73 accumulated in the cytoplasm at a level higher than in the nucleus in association with the severity of renal dysfunction and proteinuria. These findings indicate that HSP73 is mainly expressed in glomerular and tubular epithelial cells in the kidney under a physiological condition, and that its expression changes from the nucleus to the cytoplasm under pathological conditions such as a protein overload to these epithelial cells.