In unilateral ureteral obstruction [UUO] the kidney is characterized by increased fibrosis and apoptosis. Both Transforming Growth Factor- [TGF-] and Angiotensin II [ANG II] have been implicated, and ANG II may mediate its effects through TGF-. Previous studies demonstrated amelioration of renal damage when either TGF- or ANG II has been individually targeted. In this study, we sought to determine whether combining 1D11 [ monoclonal antibody to TGF-] and an ACE inhibitor, enalapril, would be more effective in UUO than either individual treatment, as has been shown in diabetic and glomerulonephritic models. Rats underwent UUO and were given either control monoclonal antibody, 1D11 or enalapril , or 1D11/enalapril combination, for 14 days. Kidneys were harvested and examined for fibrosis [trichrome; collagen (real time PCR, Sircol assay) and Fibroblast specific protein (FSP-1) expression (immunohistochemistry), apoptosis [TUNEL], macrophage infiltration [immunohistochemistry] and TGF- expression [real time PCR and tubular localization with immunohistochemistry]. UUO was found to induce fibrosis, apoptosis, macrophage infiltration and TGF- expression in the obstructed kidney. Administration of either 1D11 or enalapril individually significantly decreased all these changes; when 1D11 and enalapril were combined, there was little additive effect, and the combination did not provide full protection against damage. The results demonstrate that, for the most part, combination therapy is not additive in UUO. This could be due the continued presence of a physical obstruction or to biochemical differences between UUO and other renal disease models. Furthermore, it suggests that other targets may amenable to pharmacologic manipulation in UUO.