The in vitro hemolytic activity of live strains and clones of trophozoites of Trichomonas vaginalis was investigated. The isolates and clones were tested against human erythrocytes of groups A, B, AB, and O, and against erythrocytes of six adult animals of different species (rabbit, rat, chicken, horse, bovine, and sheep). Results showed that each of the isolates and clones tested lysed all human blood groups, as well as rabbit, rat, chicken, horse, bovine and sheep erythrocytes. No hemolysin released by the parasites could be identified. Hemolysis did not occur with trichomonads culture supernatants, and either with sonicated extracts of T. vaginalis, and nor with previously killed organisms