OBJECTIVE The mouse renal cell carcinoma line, Renca, is insensitive to transforming growth factor-beta (TGF-beta) in vitro. The present study was conducted to determine whether removal of TGF-beta from these tumor cells would inhibit tumor progression in vivo. METHODS TGF-beta elimination was accomplished either by administration of neutralizing TGF-beta antibody into mice receiving intravenous injection of Renca tumor cells or infection of TGF-beta antisense expression vector into these tumor cells before subcutaneous injection into recipient mice. RESULTS Although a low dose of TGF-beta antibody (5 mg/kg every 3 days) was without any effect, a high dose of TGF-beta antibody (50 mg/kg every 3 days), administered to recipient mice, resulted in a significant reduction in lung metastasis and was accompanied by increased apoptosis in the tumor cells. When the tumor cells were transfected with a TGF-beta1 antisense expressing vector, a significant reduction occurred in the tumor incidence, as well as the tumor burden. However, in nude mice, cells with reduced TGF-beta1 production grew almost as well as did the unmodified Renca cells, suggesting that the host's immune system might play an antitumor role. CONCLUSIONS These results indicate that progression of Renca tumor can be inhibited by eliminating TGF-beta from the tumor cells. Our results also suggest that, although insensitive to TGF-beta under in vitro conditions, Renca tumors could be inhibited by TGF-beta removal through the systemic host environment.