Clinical and laboratory findings at the time of diagnosis were correlated with the survival of 242 patients with chronic myelocytic leukemia. Twelve patients with the blastic stage of the disease (blasts 2 20%) had a median survival of eight months. Of the nonblastic patients, 28 without the Philadelphia chromosome had a relatively constant mortality averaging 43% per year and a median survival of 13 months, markedly worse than the Phl-positive group (mortality, 6% in the first year, 17% in the second year, and then 25% per year, with a median survival of 43 months; P < 0.001). In the latter group of 202 patients, features reflecting the "quantity" of leukemia (leukocyte count, marrow cellularity, and M:E serum B,,, different degrees of splenomegaly, presence or absence of symptoms) had weaker or short-term correlations with mortality, while "qualitative" abnormalities (e.g., increased percentage of circulating blasts, extramedullary leukemic tumors, major abnormalities of erythropoiesis or platelet production, marked basophilia or eosinophilia) had strong and persistent correlations with mortality. Chromosome abnormalities in addition to the Ph' appeared to have a delayed though significant effect on survival. Serum alkaline phosphatase and SGOT levels did not correlate significantly with survival, but major elevations of serum LDH were associated with increased mortality throughout the course of the disease.