In 1980, the French Cooperative Group on Chronic Lymphocytic Leukemia started a randomized clinical trial in which intermediate prognosis patients (stage B) received either an indefinite course of chlorambucil (0.1 mg/kg/d) or 12 cycles of the COP regimen (vincristine, cyclophosphamide, and prednisone). We present the results of the third interim analysis based on 291 patients (151 in the chlorambucil group and 140 in the COP group) with a mean follow-up of 53 months at the reference date of June 1, 1987. At this date, 129 deaths were observed, 65 in the chlorambucil group and 64 in the COP group; there was no improvement in overall survival with the COP regimen (P = .44) even after adjusting for both prognostic and imbalanced factors (P = .24). The 3-year and 5-year overall survival rates were, respectively, 69% and 44% in the chlorambucil group as compared with 73% and 43% in the COP group. The median survival times were 58 months in the chlorambucil group and 57 months in the COP group. Moreover, no significant difference was observed between the two treatment groups in terms of either treatment response, 9-month status, time to disease progression to stage C, or causes of death.