The electrochemical polymerization of methylene blue in aqueous solutions and the properties of the resulting films were investigated. The films possessed monomer-type redox activity, and a new redox couple, responsible for the semiconducting properties of the polymer, was observed. The growth rate of the film increased in basic media. The influence of hydroxide ions can be simulated in terms of both nucleophilic catalysis and a shielding effect. The bioelectrochemical oxidation of glucose at methylene blue semiconductor films in the presence of glucose oxidase was observed.