FISH analysis demonstrating multiple copies ofMLL in t-AML of patient RUPN 84. Digoxygenin-labeledMLL YAC probe (Oncor) was hybridized to metaphase spread. Centromeric and telomeric signals are detected on der(11) chromosome (9 o'clock). Signals also are detected on der(5) chromosome (6 o'clock) and on normal chromosome 11 (3 o'clock). There are 5 discrete signals on nearby interphase nucleus. Five or 6 signals consistently were detected on hybridization of MLL YAC probe with other metaphase spreads from the t-AML.