The study of the physiology, nutrition, antigenic structure and pathogenicity of single strains of Trichomonas vaginalis, and of their lack of sensitivity to certain antibiotics depends on the possibility of isolating these parasites “in vitro” from other associated microorganisms. The trichomonads are easily isolated from concomitant bacteria when specific antibiotics are used (Adler and Pulvertaft, 1944; Johnson and Trussell, 1945; Williams and Plastridge, 1946). To eliminate bacterial contamination from the broth cultures of Trichomonas vaginalis or T. foetus, these authors noted that the addition of 100 I.U. of penicillin and 100 µg. of streptomycin is sufficient. However a method for the rapid separation of T. vaginalis from bacterial as well as other vaginal organisms has not hitherto been described. T. vaginalis, particularly during pregnancy of the carriers, is often associated with species of the genus Candida. These yeast-like fungi are not sensitive to the commonly available antibacterial antibiotics. Anaerotropism (Magara et al., 1953) and motility of the trichomonads facilitate their isolation from fungi.