In this study, magnesium concentrations were measured in lymphocytes from patients with acute myeloblastic leukemia (AML), chronic megalositer leukemia (KML) and acute lymphoblastic leukemia (ALL) before and after chemotherapy management, and results were compared with those of control subjects. Magnesium concentrations were higher in the patient groups compared with control values. However, no meaningful differences were found among magnesium concentrations of the patient groups themselves. Similarly, no statistically meaningful differences were found between lymphocyte magnesium concentrations before and after chemotherapy management in the patient groups. In the inter-correlation analysis, we observed no correlations between pre- and post-magnesium concentrations in patients' lymphocytes. It has been suggested that magnesium concentrations of leukemic lymphocytes might increase due to the high ATP requirement of the leukemic cells since magnesium is known to play an important part as a cofactor in most of the energy-producing reactions.