In order to establish the role of the different PI3K catalytic subunits in sustaining leukemic cells proliferation and survival, we investigated by Western blot analysis the baseline expression of Bcr-Abl and its substrate CrkL, the PI3K catalytic subunits and the key enzymes of the PI3K/Akt/mTOR network in three B-ALL cell lines (TOM-1, BV-173 and SUP-B15). The gene discussed is MTOR; the disease is acute lymphoblastic leukemia.