Inoculation of alloantigenic P815 tumor cells into the vitreous cavity of eyes of BALB/c mice resulted in the intraocular development of progressively growing tumors. We observed by clinical and histologic examination that the tumors acquired a blood supply, lacked significant necrosis or degeneration, and gradually penetrated the globe into the orbit. Mice bearing these intraocular tumors did not develop tumor-specific delayed hypersensitivity (DH), and their spleens contained lymphocytes capable of suppressing tumor-specific DH when transferred adoptively into naive, syngeneic recipients. The authors conclude that the vitreous cavity (VC) is an immunologically privileged site for histoincompatible tumor cells and that the privilege is mediated by active suppression of DH, similar to anterior chamber (AC)-associated, immune deviation.