The heme-containing undecapeptide microperoxidase-11 was immobilized as a monolayer on gold wire electrodes by carbodiimide coupling of the peptide to a cystamine monolayer. Direct communication between the electrode and the heme center was observed in acetonitrile and ethanol. The observed formal potential for the Fe-III/Fe-II couple for the immobilized microperoxidase-11 was -0.290 V vs. SCE in acetonitrile and -0.286 V in ethanol. These electrodes were applied as amperometric sensors for organic peroxides in acetonitrile and ethanol. The electrocatalytic reduction of cumene hydroperoxide, t-butyl hydroperoxide and hydrogen peroxide was demonstrated. In acetonitrile, kinetic parameters (K-m and I-max) were evaluated using a modified Michaelis-Menten analysis for the electrocatalysis of the reduction of cumene hydroperoxide, t-butyl hydroperoxide and hydrogen peroxide.