Benzoyl peroxide and cumene hydroperoxide (CHP) are reduced at the anodically polarized dropping mercury electrode, the former at about +0.3 volt vs. S.C.E., and the latter at +0.1 v. Their half-wave potentials as well as that of the two reduction steps of dissolved oxygen are gradually shifted towards more negative values with increasing concentration of organic peroxides. The polarographic method is suitable for determining these peroxides in concentrations up to 2 × 10−3 mole per liter. Dissolved oxygen does not interfere seriously with the analyses.