Previous research has shown that i.p. injection of rats with pyridine results in a significant increase in immunoreactive renal cytochrome P4502E1 (alcohol-inducible form) in a dose- and time-dependent manner. However, the cellular location of renal P4502E1 in rats was not reported. Thus, it was not known whether the pyridine-induced increase in renal P4502E1 resulted from increased production of the enzyme in cells which normally express P4502E1 or from de novo expression in cells normally devoid of the protein. To address these questions, rats were injected i.p. with either 200 mg pyridine/kg body wt./day for 1, 2, 3, or 4 days (n = 2/group) or injected once with an equal volume of sterile, pyrogen-free saline (control group; n = 2). Kidney tissue samples from saline- and pyridine-exposed rats were processed by light microscopy and were immunochemically stained to detect rat cytochrome P4502E1. Most of the immunoreactive P4502E1 was located within renal cortical epithelial cells lining proximal and distal tubules of the cortex with lesser--but consistent--amounts present in tubular epithelial cells within the inner and outer medulla. Pyridine exposure resulted in a 2-3-fold increase in P4502E1 immunoreactivity in proximal cortical tubules surrounding glomeruli and cortical blood vessels. The results of this study demonstrate a cell-specific distribution of cytochrome P4502E1 within the rat kidney and indicate that pyridine exposure results in a selective induction of immunoreactive P4502E1 in tubule epithelial cells which constitutively express this enzyme. The results of this study provide a morphologic basis for interpreting cell-specific nephrotoxicity due to xenobiotics that are biotransformed to toxic metabolites by renal P4502E1.