Leukemic lymphoblasts generated by a single leukemic cell in vitro undergo apoptosis when separated from stroma. Cells from case no. 3 cultured for 12 months on stroma were studied before and after detachment from stroma for 7 days. Light scattering dot plots (top) illustrate measurements of forward light scattering (FSC; X axis), which indicates cell size, and side light scattering (SSC; Y axis), which indicates cell granularity. The gates shown encompass morphologically undamaged lymphoblasts (72% of all cells in the stroma-supported culture; 5% after detachment from stroma). Double color dot plots (bottom) illustrate binding of Annexin V (X axis), a marker of apoptosis, and staining with propidium iodide (Y axis), an indicator of cell membrane permeability, of cells within the gate. Viable cells are confined to the bottom left quadrants.