Transforming growth factor-β (TGF-β) is a profibrotic cytokine which has been implicated in the renal fibrosis which follows unilateral ureteral obstruction (UUO) in the rat. TGF-β receptor type I (TGF-RI) and TGF-β receptor type E II (TGF-RII) are part of the complex which mediates the response to TGF-β. We sought to determine if TGF-RI and TGF-RII are found in the kidney, and if their expression is changed as a result of UUO. Polymerase chain reaction (PCR) was used to determine expression of mRNA for TGF-RI and TGF-RII in the kidney. Immunoperoxidase was used to localize and quantify the expression of these receptors at 3,7,14,21 and 28 days after UUO, and in sham-operated animals. Expression of mRNA for TGF-RI and TGF-RII was demonstrated in sham operated, obstructed and contralateral unobstructed kidneys using PCR. Using immunoperoxidase, a uniform distribution of TGF-RI and TGF-RII was found in cortical tubules of sham operated kidneys, whereas medullary tubules showed a patchy TGF-RI distribution and no TGF-RII staining. After UUO, an increased tubular expression of TGF-RI and TGF-RII was noted in both obstructed and contralateral kidneys compared to sham operated kidneys. No staining for either TGF-RI or TGF-RII was noted in glomeruli, vasculature or interstitial cells. TGF-β receptors I and II were found exclusively in renal tubules and were shown to increase in both the obstructed and contralateral kidneys relative to sham operated animals. Upregulation of TGF-β receptors in both kidneys suggests that TGF-β may contribute to the fibrotic response in the obstructed kidney and the hypertrophic response of the contralateral kidney.