The Fenton reagent (hydrogen peroxide plus Fe(II) or Fe(III) catalyzes nearly quantitative conversion of amino acids to ammonia and a mixture of aliphatic aldehydes and carboxylic acids containing one less carbon atom. The oxidation is stimulated by bicarbonate ion and additionally by either EDTA, EGTA, o-phenanthroline, Desferal, Ferrozine, DETAPAC, NTA, citrate, or ADP when they are present at concentrations below that required to chelate all of the iron present. With excess chelator, amino acid oxidation occurs only after a lag which corresponds to the time required to reduce (by oxidation) the concentration of chelator to a level slightly below that needed to chelate all of the iron. The results suggest that amino acid oxidation requires the participation of both an iron-chelate and either unchelated iron or a second type of iron complex, possibly one involving bicarbonate ion and/or the amino acid. Low sensitivity of amino acid peroxidation to various radical scavengers indicates that oxygen radicals are either not involved or are generated in situ by peroxidation of an iron-chelate-amino acid complex. The formation of such a complex was established in spectrophotometric studies showing that Fe(II), ferrozine and an amino acid react to form first a ternary complex which subsequently decomposes to yield the typical (ferrozine)3-Fe(II) complex. The amino acid-Fe(II)-ferrozine-complex but not the (ferrozine)3-Fe(II) complex is readily oxidized by hydrogen peroxide.