The aim of this study was to evaluate ROS production, sulfane sulfur levels, the expression of proteins with antioxidant properties, such as L-cysteine-metabolizing enzymes (cystathionine β-synthase, CBS; cysteine dioxygenase 1, CDO1; cystathionine γ-lyase, CTH; 3-mercaptopyruvate sulfurtransferase, MPST; thiosulfate sulfurtransferase, TST) and non-enzymatic proteins (p53; transferrin receptor 1, TfR1), in human brain cancer cells differing in malignancy: 1321N1 astrocytoma and T98G glioblastoma. The gene discussed is CDO1; the disease is astrocytoma (excluding glioblastoma).