Survival curves of CML patients treated with IFN-α2b or hydroxyurea only, related to the Sokal prognostic score, and shown for the different prognostic groups separately. 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. Only for the group with an unfavorable risk profile (Sokal score >1.2) is a trend (log-rank, P = .20; Breslow, P = .03) for better survival seen in favor of IFN therapy.