The treatment of chronic myelogenous leukemia (CML) with specific tyrosine kinase inhibitors typically results in clinical success, although therapeutic failure frequently occurs. In order to investigate the biological consequences of treating CML cells with such drugs, we previously reported that the antioxidant selenoprotein glutathione peroxidase-1 (GPx-1) was induced by imatinib in both patient samples and cultured cells. Here, we extend these findings to demonstrate that the treatment of CML cell lines, but not non-CML cells, results in an approximately four-fold increase in the levels of another important antioxidant protein, manganese superoxide dismutase (MnSOD), without altering the steady state levels of the corresponding transcript.