Antileukemia T-cell lines are capable of lysing syngeneic leukemia cells in the presence of bone marrow stroma. Stromal cell layers were established as described in Materials and Methods. Cell-mediated cytotoxicity was measured using the ⁵¹Cr release assay and is represented as a percentage of specific lysis. The results shown are from 2 patients representative of 4 independent experiments (4 different patients) and correspond to an effector:target ratio of 40:1. On the lower panel, stromal cells were labeled with⁵¹Cr and used as target cells.