In this study we tested whether the pattern of cytokines expressed by human carcinomas could account for a different in vivo recruitment of leukocyte subpopulations as a part of the anti-tumor immune response. Two carcinoma cell lines, SK- OV-3 ovary carcinoma and CALU-3 lung carcinoma, were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR), immunofluorescence and ELISA for the expression and in vrtro production of cytokines with chemotactic, pro- inflammatory and growth-stimulating activity. Although both cell lines displayed a constitutive expression of granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage- CSF (GM-CSF), M-CSF, interleukin (IL-) la and IL-8, only CALU-3 cell line expressed IL-10, RANTES (Regulated upon Activation, Normal T Expressed and Secreted) and monocyte- activating protein (MCP)-I. MCP-I and IL-8 were detected by immunohistochemistry on sections from tumors xenografted in nude mice. To analyze whether the tumor-released cytokines modulate leukocytes in tumor infiltration, we studied the distribution of human peripheral blood leukocytes injected in the proximity of SK-OV-3 and of CALU-3 tumor xenografts. While SK-OV-3 was unable to recruit human leukocytes and appeared to be barely infiltrated by murine CD45+ cells, CALU-3 appeared to be rapidly and heavily infiltrated by human leukocytes which induced tumor necrosis within 18–24 hr. © 1995 Wiley-Liss, Inc.