Constitutive tyrosine kinase activity of Bcr-Abl promotes proliferation and survival of chronic myelogenous leukemia (CML) cells. Inhibition of Bcr-Abl tyrosine kinase activity or signaling proteins activated by Bcr-Abl in CML cells blocks proliferation and causes apoptotic cell death. The selective Abl kinase inhibitor, STI-571 (marketed as Gleevec), is toxic to CML cells in culture, causes regression of CML tumors in nude mice, and is currently used to treat CML patients. Here we describe a p.o. active, dual Src/Abl kinase inhibitor with potent antiproliferative activity against CML cells in culture. This 4-anilino-3-quinolinecarbonitrile (SKI-606) ablates tyrosine phosphorylation of Bcr-Abl in CML cells and of v-Abl expressed in fibroblasts. SKI-606 inhibits phosphorylation of cellular proteins, including STAT5, at concentrations that inhibit proliferation in CML cells. Phosphorylation of the autoactivation site of the Src family kinases Lyn and/or Hck is also reduced by treatment with SKI-606. Once daily oral administration of this compound at 100 mg/kg for 5 days causes complete regression of large K562 xenografts in nude mice.