AbstractThis article reviews recent findings that bear on the mechanism(s) of tumor‐specific Lyt‐1+2−T cell‐mediated tumor eradication in vivo A tumor‐immune Lyt‐1+2−T cell subset has been identified which is distinct from T cells mediating in vitro cytotoxicity (Lyt‐1+2+/1−2+). The Lyt‐1+2−cells have a crucial role in rejecting tumor cells when adoptively transferred into T cell‐deprived B cell mice. This indicates that Lyt‐1+2−T cells do not necessarily require recruitment of the host's cytotoxic T cell precursors for implementation of in vivo immunity. Instead, this T cell subset exerts its anti‐tumor effect in collaboration with macrophages as shown with an in vivo tumor cell culture system utilizing a diffusion chamber. A pathway of Lyt‐1+2−T cell‐macrophage interaction leading to tumor cell killing is discussed in terms of its probable relevance to the eradication of tumor cell masses consisting of tumor cells expressing quantitatively and/or qua