The aim of our study was to assess the correlation between ROS production, sulfane sulfur levels, and the expression of enzymatic proteins (CBS, CTH, TST, MPST, CDO1) and non-enzymatic proteins (TfR1, p53) involved in L-cysteine and iron metabolism, in human brain cancer cells differing in the degree of malignancy, such as 1321N1 (low-grade malignant astrocytoma) and T98G (grade IV glioblastoma multiforme). The gene discussed is CDO1; the disease is glioblastoma.