Fourteen patients with chronic myelogenous leukemia in chronic phase who had achieved hematological remission after alpha-interferon (IFN) therapy were evaluated for their ability to form hemopoietic colonies in vitro. Patients were studied both before and after discontinuation of IFN to assess the optimal timing for a further therapeutic approach consisting of stem cell collection followed by autologous bone marrow transplantation (ABMT). Before stopping IFN a profound inhibition of CFU-GM and BFU-E growth was observed. The numbers of CFU-GM and BFU-E in the bone marrow recovered to 50 per 2 x 10(5) cells plated at a median of 158 and 122 days, respectively, after stopping IFN. At that time, 12 patients were submitted to stem cell harvest and subsequently to ABMT. All patients showed complete engraftment and hematological reconstitution; cytogenetic improvement was observed in eight (67%) cases; two patients displayed complete disappearance of the Ph1 chromosome, confirmed at the molecular level. Eleven of the 12 patients are still in hematological remission at a median of 18 months from autografting and a median of 48 months from diagnosis.