A chemical model for the H 2 O 2 promoted oxidation by nitric oxide synthase (NOS) has been developed. Biomimetic oxidations were carried out using H 2 O 2 and tetrakis(perfluorophenyl)porphyrinato-iron(III) chloride (FeTPPF 2 0 ) as a catalyst. Similarly to NOS our model system produces N δ -cyanoornithine, citrulline and NO from NOHA and did not oxidize arginine itself. Based on these results we propose a peroxide shunt to be involved in the catalytic cycle of NOS. To the best of our knowledge this is the first chemical system that semiquantitatively mimics NOS activity.