5A7 but not 3G3 separates apoptotic HL-60 cells from nonapoptotic ones. Two-dimensional flow cytometric analyses of DNA-topo IIβ contents are performed on logarithmically growing (A and C) and Ara-C–treated HL-60 cells (B and D) using topo IIβ-specific monoclonal antibodies, 5A7 (A and B) and 3G3 (C and D).