Subpopulations of tumor infiltrating leukocytes in immunogenic skin tumors were identified with monoclonal antibodies. The tumors studied included primary UV-induced tumors and JB/MS melanomas, which survive in the host by immunosuppression of the immune response. The proportions of nucleated cells in primary UV-induced tumor cell suspensions which reacted with monoclonal antibodies were: 52% Mac-1+, 21% Lyt-1+, 13% Lyt-2+, 7% L3T4+, and 8% IL-2R+. Thus there was a high proportion of cells of the macrophage lineage in the growing UV-induced tumors. In JB/MS melanoma cell suspensions the mean proportion of macrophages was 6.4%, and total T lymphocytes (Lyt-1) averaged only 5.5%. Thus, there was little leukocytes infiltration into JB/MS melanoma, suggesting that chemotaxis was defective. The high level of macrophages and T cells in the primary UV-induced tumors indicates that chemotaxis was intact. Therefore, either the tumorcidal capacities of the macrophages and Tc were insensitive to activated macrophages and to Tc cells
