A highly immunogenic C3H-derived UV-induced tumor was cotransfected with a murine transforming growth factor type beta 1 (TGF-beta 1) cDNA and a neomycin-resistance gene. Stable clones were isolated and used in vitro and in vivo to determine the effects of endogenously produced TGF-beta on cytolytic T-lymphocyte (CTL) responses. Tumor cells producing TGF-beta, though retaining expression for class I major histocompatibility complex molecules and the tumor-specific antigen, did not stimulate primary CTL responses in vitro and were not effective in vivo for directly stimulating primary CTL or in priming for CTL responses. Furthermore, TGF-beta-producing tumors grew progressively in transiently immunosuppressed mice without losing the tumor antigen; thus, TGF-beta produced by tumors may promote escape from immune surveillance.