We have investigated glucocorticoid receptor (GR) level, terminal deoxynucleotidyl transferase (TdT) activity and the initial responsiveness to prednisone and vincristine in 31 patients with acute lymphatic leukemia (ALL) and with chronic myelogenous leukemia in blast transformation (CML/BT). All 11 patients with low levels of GR (5,000 binding sites per cell) were resistant to this initial treatment whereas 13 of the 20 patients with high levels of GR responded readily. The correlations between clinical responsiveness and TdT activity were significant to the p less than 0.005 level but there was no linear correlation (r = 0.3427) between GR-level and TdT activity. High levels of both GR and TdT seemed to be associated with better prognosis in patients with these leukemias. Thus the determination of GR and TdT might help selection of patients likely to respond to prednisone and vincristine in ALL and CML/BT.