Manganese is oxidized by a wide variety of bacteria. The current state of knowledge on mechanisms and functions of Mn2+oxidation in two strains ofPseudomonas putida, inLeptothrix discophoraSS-1, and inBacillussp. strain SG-1 is reviewed. In all three species, proteins bearing resemblance to multicopper oxidases appear to be involved in the oxidation process. A short description of the classification of Cu centers is followed by a more detailed review of properties and postulated functions of some well-known multicopper oxidases. Finally, suggestions are made for future research to assess the potential role of multicopper oxidases in bacterial Mn2+oxidation.