The melanoma reactive chimeric 14.18 (ch14.18) antibody can mediate enhanced in vitro lysis of human M-21 melanoma cells. This study analyzes the antitumor effects and the in vivo binding of ch14.18 antibody with M-21 melanoma cells in severe combined immunodeficiency (SCID) mice. Outgrowth of tumors was prevented in 6/6 animals by the simultaneous subcutaneous injection of peripheral blood mononuclear cells (PBMC) [3 x 10(6) cells (2 animals); 10 x 10(6) cells (2 animals); and 30 x 10(6) cells (2 animals)], with 0.5 mg ch14.18, 1,500 U interleukin 2 (IL-2), and 10(6) M-21 cells. In contrast, 7 of 7 control mice that received M-21 cells alone, 7 of 7 mice that received M-21 cells and ch14.18, and 5 of 6 mice that received M-21 cells plus PBMC plus IL-2, grew subcutaneous tumors. The in vivo localization of ch14.18 was then evaluated in an intraperitoneal (i.p.) tumor model, where 0.3 cm melanoma nodules develop within 3 weeks after the i.p. administration of M-21 cells. Flow cytometric and immunohistochemical analysis revealed the GD2 antigen present throughout the tumor nodule. Intraperitoneal administration of 0.01, 0.1, or 1.0 mg of ch14.18 to SCID mice previously engrafted i.p. with M-21 cells resulted in detectable ch14.18 binding to tumor cells in vivo within 10 hours of antibody administration. Ch14.18 penetration was limited to approximately 20 cell layers, demonstrating that ch14.18 has limited access to some cells in large tumor nodules. This study demonstrates that the addition of ch14.18 to IL-2 and human effector cells can result in significant antitumor activity by preventing the establishment of tumor nodules. These results suggest that clinical testing of IL-2 plus ch14.18 might be most effective if used in the setting of microscopic residual disease. Therapies that enhance ch14.18 penetration into tumor nodules should be evaluated with ch14.18 for patients with advanced melanoma.