A review of the literature on the history of Trichomonas vaginalis and studies on differences among T. vaginalis strains was carried out. A need for the study of the characteristics that might help identification of trichomonads in general and T. vaginalis in particular was noted. Studies on isoenzyme variants revealed four enzymes that could be useful in distinguishing between different trichomonads and among different strains of T. vaginalis. These were lactate dehydrogenase, malate dehydrogenase, hexokinase and glucose phosphate isomerase. Using these four enzymes, it was possible to divide most strains of T. vaginalis into 5 groups. the isoenzyme results is discussed. It was possible to seek correlation between iso-enzyme differences and other biological properties such as concanavalin A-induced agglutination and generation time of the parasites; stroni correlation between these pro-perties and the previously divided group were found. Isoenzyme studies on flagellates isolated from faeces of monkey showed them to be very different from T. vaginalis; electron microscopy revealed that these organisms are probably a Trichomitus species. The results of isocnzyme and other studies on some unusual T. vaginalis strains are also discussed. Investigation into isolation, cloning and staining for light microscopy studies were also under-taken.