Ascorbic acid (AA) enhanced As₂O₃-induced apoptosis in su-DHL-4 (A,B) and HL-60 cells (C,D). Cells were treated with 1 μmol/L As₂O₃, 62.5 μmol/L AA alone or together. Cell viability and apoptotis were determined as described in Materials and Methods. Values are the mean of three independent experiments.