The human cytotoxic T cell line TALL-104 displays potent anti-tumor effects in animals with spontaneous and induced malignancies. We investigated the biodistribution of TALL-104 cells in tumor bearing and healthy mice. 111In-labeled TALL-104 cells, injected intravenously, localized primarily in the lungs for the first 2 h, and redistributed to liver, spleen, and kidneys in the following 24 h both in immunodeficient and immunocompetent mice. TALL-104 cells consistently accumulated in the tumor and at sites of metastases. In animals injected with free 111In-oxine, most of the radioactivity remained in the blood pool with no significant organ accumulation. These data support the tumor homing properties of TALL-104 cells, information which is crucial to their therapeutic efficacy in forthcoming clinical trials.