Lymphoma B cells undergo apoptosis after irradiation or staurosporine treatment. Lymphoma cells (FL-2 patient) were cultured for 4 hours or 18 hours (A) without treatment or after irradiation (3,000 rads), (B) with 5 μmol/L staurosporine or dimethyl sulphoxide (DMSO) as a control. Cells were stained with annexin V-FITC/PI and then analyzed by flow cytometry. Numbers within dot plots represent the percentages of cells in early apoptosis (lower right, annexin V⁺/PI-) and in late apoptosis or in necrosis (upper right, annexin V±/PI⁺). Percentages next to the dot plots indicate the specific apoptosis.