Vaginitis/vaginosis is an extremely common medical problem. Most cases are caused by yeast (predominantly Candida albicans), the protozoan Trichomonas vaginalis, or a specific mixture of bacteria (bacterial vaginosis). The prevalence of each of these varies with the patient population. The clinical signs used in differentiating among these and the associated bacterial flora are shown in Table 3. Because vaginitis/vaginosis cannot be adequately diagnosed solely on the basis of symptoms or physical examination, some laboratory methods are required. Yeast vaginitis is diagnosed by microscopic detection of budding yeast or pseudohyphae in vaginal secretions. The most sensitive method for detection of Trichomonas vaginalis is culture, but microscopic methods are more commonly used. Wet-mount examination for motile trichomonads is the least sensitive microscopic method. The sensitivity is increased when fluorescent monoclonal antibodies are used. Bacterial vaginosis may be diagnosed in the clinic by detecting three or more of the following on examination: (1) homogeneous adherent discharge, (2) vaginal fluid pH greater than 4.5, (3) amine odor, and (4) clue cells. A diagnosis may also be made by detecting the replacement of lactobacilli by a mixed presumably anaerobic flora. This is accomplished by examining a Gram stain of vaginal fluid. It is not uncommon for a woman to have more than one microbial source for her vaginal signs and symptoms. A vaginal examination should include appropriate tests for detection of all three of these agents.