The current treatment of trichomoniasis is based on the use of 5-nitroimidazole derivatives. Although metronidazole is reliable, inexpensive and highly effective against anaerobic microorganisms and protozoa, the development of metronidazole-resistant T.vaginalis strains pose to an increasing problem. Nitroimidazoles are compounds having azomycin (2-nitroimidazole) chemical structure and are obtained from Streptomyces strains. Benzimidazole, which is found in the structure of proton pump inhibitors, is also present in the other components that have antiprotozoal activity. In this study, the in vitro susceptibility of T.vaginalis against metronidazole, ornidazole, and the proton pump inhibitors which are tested recently as antiprotozoal agents; pantoprazole and esomeprazole was investigated. For this purpose a clinical T.vaginalis strain which was formerly isolated and stored after cryopreservation process in our laboratory was used. Minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC) values of those agents against to this strain were determined in vitro by dilution method in 24-well cell culture plates. Trypticase yeast extract maltose medium, horse serum and antibiotic (penicillin + streptomycin) were distributed to each well of cell culture plates and after metronidazole, ornidazole, pantoprazole and esomeprazole solutions were added to two wells for each as 800, 400, 200, 100, 50 and 25 mu g/ml, followed by the addition of 1 ml 5x10(3) T.vaginalis trophozoites into each well. Plates were incubated at 37 degrees C, and viability and motility of the trophozoites were evaluated under light microscope at 24, 48 and 72 hours after incubation. MIC and MLC values of metronidazole/ornidazole in the 72th hour were found as 50 mu g/ml and 100 mu g/ml, respectively. MIC and MLC values for pantoprazole in the 72th hour were 200 mu g/ml and 400 mu g/ml, while the values for esomeprazole were 400 mu g/ml ve 800 mu g/ml, respectively. As a result, T.vaginalis strain used in the study was susceptible to metronidazole and ornidazole, besides, it was considered that pantoprazole and esomeprazole were also effective to the parasite and could be used as alternative drugs. However, further in vitro and clinical studies are clearly needed on the antiprotozoal effects of proton pump inhibitors. To our knowledge, this study was the first in literature, which esomeprazole's susceptibility on T.vaginalis was investigated in vitro.