A series of enzymatic studies was conducted on the carbohydrate metabolism of T. vaginalis employing cell-free extracts. The results provide evidence for the existence of a functional Embden-Meyerhof pathway in glucose dissimilation. The principal product of anaerobic glycolysis, lactic acid, was produced in high concentration. Analysis of cellular material showed that T. vaginalis contained a high glycogen content, 17% of the dry weight of the cell. Trichomonas vaginalis, an anaerobe, is one of a few nonchlorophyll-containing, protozoans capable of fixing carbon dioxide. Almost the entire amount of radioactive carbon dioxide supplied during the course of growth was found to be fixed in lactic acid. No significant portion of radioactivity remained within the cell. Degrading the lactic acid, only the carboxyl carbon was found to be labelled. Various aspects of the fixation mechanism were investigated. Chemical analyses and isolations were carried out on the protoplasm to provide additional information concerning the physiology of this protozoan parasite. Studies of this nature may some day provide a clue leading to the chemotherapy of trichomoniasis.