A case of malakoplakia of the prostate is presented. Electron microscopic appearances support the origin of the Michaelis-Gutmann bodies from phagolysosomes in the histiocytes characteristic of the lesion. Biochemical analysis revealed the presence of muramic acid in the prostate with malakoplakia. This amino sugar is characteristic of bacterial cell walls and despite the absence of demonstrable bacteria in the affected tissues indicates the involvement of bacteria in the disease process.