In a study using human IFN-alpha, 36 of 51 patients with chronic phase CML achieved a complete hematologic remission. More significantly, 20 patients showed suppression of Ph-positive metaphases with reappearance of cells with normal karyotype. To date, the authors have treated 44 chronic phase CML patients with recombinant IFN-alpha as their frontline biologic therapy with similar hematologic and cytogenetic responses. Gamma interferon is active against CML but less so than IFN-alpha. Chemotherapy followed by IFN-alpha also shows promise. Interferons have produced only limited responses in terminal phase CML patients.