AML samples show widely variable levels of spontaneous, untreated apoptosis, but certain cytogenetic subtypes consistently demonstrate low apoptosis, relative to normal myeloid cells. Apoptosis frequencies are expressed relative to nonapoptotic cell frequencies. Shaded area denotes levels of spontaneous apoptosis measured in normal myeloid cells in six different control bone marrows (also shown in Fig 2). Median apoptosis for each AML subgroup is denoted by arrows on AML sample ranges and is expressed numerically. Samples with simple karyotypic abnormalities, including (15; 17), (8; 21), and (9; 11) translocations, chromosome 16 inversions, and chromosome 7 deletions, were tested, as were samples with many cytogenetic abnormalities and samples with normal or undescribed karyotypes. Sample numbers in each cytogenetic subgroup are denoted.