Survival curves from the first year on of CML patients treated with IFN-α2b or hydroxyurea only, related to WBC control during the first year of therapy. Only data from patients with 6 or more analyses during this period were used. Curves are based on the intention to treat, regardless of any protocol violation or cause of death. Data on those patients that underwent BMT during chronic phase were censored as of the date of transplantation.