The mechanism for the reaction between an intradiol dioxygenase and a hydroperoxy probe was modeled with the DFT method - B3LYP. Five models of the iron cofactor - probe complexes differing in the total charge and the number of ligands bound to iron were considered. The most important conclusion from the study described in this contribution is that the critical O-O bond cleavage, leading to the alkoxyl radical intermediate, most likely does not yield the reactive oxoferryl species. Instead, in the preferred reaction channel the peroxo group is protonated and the O-O cleavage leads to the ferrous complex with one of the tyrosine ligands oxidized to the tyrosinate radical. The factors affecting the product specificity are also discussed in the paper. (C) 2010 Elsevier B. V. All rights reserved.