It was shown that ceruloplasmin, apart from the known oxidative conversion of dopamine into melanin, can also produce (DHI)‐melanin from 5,6‐dihydroxyindole and THP‐melanin from tetrahydropapaveroline. Ceruloplasmin acts as an oxidase and the kinetic parameters for these oxidative reactions are reported. Since these ceruloplasmin‐catalyzed reactions occur also at pH 7.4, they could have a significant physiological impact. This ceruloplasmin‐oxidasic activity is enhanced by copper ions and inhibited by chelators, such as ethylenediaminetetraacetic acid (EDTA) and desferoxamine (DEF). Some possible implication of melanin production in blood are discussed.