The method has been successfully employed in the diagnosis of Trichomonas vaginalis infection of the female genital tract. This parasite was found by phase-contrast microscopy in 47 % of 1,000 women examined at a police court clinic. Fixative slide preparations were also obtained from these women at the time of their medical examination. Of these specimens, 38x6% showed the presence of Tr. vaginalis, and 10 % were also found to be infected with N. gonorrhoeae.The fixative slide technique may also prove of value in such widely separated fields as exfoliative cytology and the diagnosis of primary syphilis.For satisfactory results in pathological investigations it is essential that the material to be studied should be either in a fresh condition at the time of examination or adequately fixed immediately after removal from the body. This is of the utmost importance in the diagnosis of malignant disease by examination of exfoliated cells, and similar requirements must be satisfied in the case of delicate protozoa and other organisms which quickly disintegrate when removed from their normal environment. When smears from tissues or exudates have to be studied the usual procedure up to now has been to spread the material thinly on a microscope slide and to fix the film so prepared in alcohol or other solution before it has time to dry. Often, however, treatment of the specimen is delayed, the film dries, and the cells are damaged. Equally unsatisfactory is the sending of dry unfixed smears to the laboratory for diagnosis of Trichomonas vaginalis infection. In order to overcome these difficulties we have devised a method which allows fixation to occur immediately the cells are brought into contact with the surface of a chemically treated microscope slide. Most of our experience so far has been gained with Trichomonas