To improve the management of chronic myeloid leukemia (CML) in a single center, we have used interferon-alpha (IFN-alpha) to treat newly diagnosed Ph-positive CML patients and investigated the factors predictive of a major cytogenetic response. Eighty-one patients with a median age of 50.5 y (17-70) were given IFN-alpha (5 x 10(6)/sqm/day, s.c.). The median interval between diagnosis and IFN-alpha was 45 days (0-160). IFN-alpha doses were adjusted to maintain the white blood cell (WBC) count between 1.5 and 5 x 10(9)/l and the platelet count between 50 and 100 x 10(9)/l. At diagnosis, Sokal's criteria were used to classify patients into three groups: low (n = 39), intermediate (n = 32) and high risk (n = 10). A complete hematological response (CHR) was achieved in 66 cases (81.5%). Cytogenetic response was evaluated in these 66 responders. Thirty-six patients (44.4%) achieved a major cytogenetic response (MCR) (> or = 65% Ph-negative cells), 31 of them having a complete cytogenetic response. The 5-y transformation-free survival (TFS) of the 81 patients was 77 +/- 14% (95% CI) and was statistically influenced by the CHR rate at three months (p = 0.008) and the achievement of MCR or CCR (p < 0.0009 and p < 0.0005, respectively). Moreover, we found that the MCR or CCR were significantly influenced by the obtaining of CHR at three months (p < 0.001 and p < 0.0001, respectively). These results show that IFN-alpha can induce high rates of hematological and cytogenetic responses when administered in doses leading to myelosuppression. The achievement of CHR within three months could be useful to identify early those patients who will not respond to IFN-alpha and who need alternative treatments such as allogeneic or autologous stem cell transplantation.