The Cr(V) products of the reaction of Cr(VI) with H2O2 were studied by EPR spectroscopy. In addition to the well-characterized tetrakis(eta(2)-peroxo)chromate(V) complex, [Cr(O-2)(4)](3-), with g(iso) = 1.9723 (A(iso) = 18.4 x 10(-4) cm(-1)), three new species were observed with isotropic EPR parameters, g(iso) = 1.9820, g(iso) = 1.9798 (A(iso) = 16.3 x 10(-4) cm(-1)), and g(iso) = 1.9764 (A(iso) = 18.1 x 10(-4) cm(-1)). While [Cr(O-2)(4)](3-) is stable at high concentrations of H2O2 and in alkaline solution, the species with a signal at g(iso) = 1.9798 is stabilized at low relative concentrations of H2O2 and in neutral solution. The signal at g(iso) = 1.9764 is most prominent in weakly acidic (pH = 4-7) solutions and low relative concentrations of H2O2. Finally, the signal at 1.9820 is only minor and is apparent at low pH values and low [H2O2]. From the pH and [H2O2] dependences, and by analogy with the V(V) chemistry, the species giving rise to the signals at g(iso) = 1.9820, g(iso) = 1.9798, and g(iso) = 1.9764 are assigned as the oxo(eta(7)-peroxo)chromium(V), [Cr(O)(O-2)(OH2)(n)](+), aquaoxobis(eta(2)-peroxo)chromate(V), [Cr(O)(O-2)(2)(OH2)](-), and the hydroxotris(eta(7)-peroxo)chromate(V), [Cr(O-2)(3)(OH)](2-), complexes, respectively. The implications of these Cr(V) peroxo species for understanding the in vitro DNA damage caused by Cr(VI) and H2O2 and the genotoxicity of carcinogenic Cr(VI) complexes are discussed.