The possibility of targeting LAK cells to the tumor by arming them with monoclonal antibodies directed against tumor associated antigens was tested in a rat model of colon carcinoma. Peritoneal carcinomatosis was generated by injection of cloned tumor cells and 111In-labeled LAK cells were injected in the tail vein after preincubation with the monoclonal antibodies themselves. It appeared that the antibodies did not significantly improve tumor targeting of LAK cells, most of the radioactivity being recovered in the spleen, the liver, the kidney or the lung, and only a small fraction in the tumor.