Ferric peroxo complexes are currently extensively studied due to their proposed occurrence as reactive intermediates in the catalytic oxygenation reactions of enzymes. An electronic structure investigation is presented for the synthetic mononuclear nonheme Fe(III)-hydroperoxo complex and the related Fe(III)peroxo compound which is based on complementary EPR and applied-field Mossbauer spectroscopy. The data provide detailed insight into the properties of the iron(III) site in the low-spin Fe-OOH compound and the high-spin Fe-OO complex.