The intracellular glutathione (GSH) content was measured in 73 patients with leukemia and compared with controls. GSH content was between 1.16 and 5.55 mumol/g protein (mean 2.96 +/- 0.86) in the study group and between 0.5 and 1.48 mumol/g protein (mean 1.31 +/- 0.27) in the control group, statistically significant difference (p = 0.0000). There was no significant difference between acute and chronic leukemias, lymphoid and myeloid leukemias and, more importantly, newly diagnosed and relapsed patients. GSH content did not change significantly with clinical and hematologic parameters such as age, sex, and initial hematologic findings. In addition, variable changes were detected over 24 h in 9 patients. It can be concluded that GSH content in leukemic cells was higher than in controls and showed a wide range. The absence of a relationship between GSH content and clinical and laboratory parameters suggested that GSH is not the sole determinant of response to cytotoxic drugs. GSH variation over a 24-hour period may be important in the timing and success of chemotherapy for leukemias.