The INDO/ROHF/CI quantum chemical method has been used to calculate the electronic structure and spectra of two candidate peroxide intermediates of model peroxidases. In the enzymatic cycle of this family of oxidative metabolizing heme proteins, hydrogen peroxide is required to transform the ferric resting state to the catalytically active, ferryl Fe=O, compound I species. While a peroxide complex has been proposed as a key intermediate in this reaction, this intermediate species is too transient to have thus fat been definitively characterized. Electronic spectra observed prior to compound I formation during the reaction of H2O2 with both wild type and the R38L mutant of horseradish peroxidase C (HRP-C) have been attributed to this intermediate. There are, however, significant qualitative differences in these spectra in the 300-450-nm region, with a "hyper-Soret" observed in one and a normal Soret, not very different from the resting stale, found in the other.