Biological tests performed using 3T3 fibroblasts indicated low cytotoxicities for the complexes mer- -, where pic = picolinate anion and Cys = cysteine. Oxidation of these complexes by hydrogen peroxide was studied in NaOH and NaHCO 3 media. Electronic (UV-Vis) and EPR spectroscopies were used to monitor the reaction course. 3-anion at pH & 8 was followed by EPR spectroscopy. Based on the obtained kinetic and spectroscopic data, mechanisms for the redox transformations of these chromium(III) complexes are proposed.