The motility of viable Trichomonas vaginalis organisms is readily demonstrable in a clinical wet mount or cultured specimens. We attempted to determine whether migration is a dynamic process such that the organisms move to avoid exposure to toxic antimicrobial agents. With the use of axenic cultures of T. vaginalis that were radiolabeled and assayed for chemotaxis in plastic multiwelled plates with a membrane filter inserted to trap organisms, the response of clinical isolates to various antimicrobial agents was studied. Chemotaxis was readily demonstrable and dependent upon factors including time of incubation, media used, and viscosity of media. Nitroimidazoles (e.g., metronidazole) which readily inhibited the growth of these organisms also caused significant chemorepulsion after minutes of exposure. The antifungal imidazoles ketoconazole and miconazole inhibited growth nearly as readily and caused chemorepulsion, but to a lesser degree. The spermicide Nonoxynol-9 also inhibited growth and caused significant chemorepulsion. The minimal concentrations of many compounds which inhibited growth were very similar to those which caused significant chemorepulsion. Imidazole and antibiotics (e.g., penicillin) which did not inhibit growth did not induce any chemotactic effects. Chemotaxis of T. vaginalis is an active and dynamic process, and the organisms display chemorepulsion shortly after exposure to toxic antimicrobial agents, well before toxicity can be demonstrated.