BACKGROUND: We thought that nitroimidazoles including metronidazole had been overused empirically for treatment of trichomoniasis in Korea. But there were not any reports about in vitro-drug susceptibility and distribution of resistant strains of Trichomonas vaginalis up to date. Therefore, we made an experiment in order to observe the susceptibility of clinical isolates of T. vaginalis to a variety of antiprotozoal agents. METHODS: Twenty-six strains of T. vaginalis isolated from 217 patients afflicted with the increased vaginal discharge were tested by Meingassner's microtiter plate method in newly devised anaerobic box, in which anaerobic and microaerobic conditions were more easily manipulated. The agents used in this study for testing the minimal lethal concentration (MLC) to the clinical isolates were as follows; nitroimidazoles, doxycycline, Zinc sulfate and gentian violet as chemotherapeutic agents and povidone-iodine as vaginal cleansing agents were studied. RESULTS: In anaerobic culture, according to anaerobic resistance cut-point (minimal lethal concentration >3.1 microgram/mL) proposed by M ller etc., metronidazole (MTZ)-, tinidazole (TNZ)-and ornidazole (ONZ)-resistant strains were four (4/26, 15.4%), two (2/26, 7.7 %) and two (2/26, 7.7%) strains, respectively. Among these resistant strains, two strains (G7 and G16) were resistant to two drugs and one strain (G20) resistant to three drugs concomitantly. Their resistance range was narrow as 6.25~12.5 microgram/mL. MLC of clotrimazole was > or = 2,000 microgram/mL in all strains, econazole was as high as 62.5~250 microgram/mL and miconazole was also high as 62.5~> or = 2,000 microgram/mL. In microaerobic culture (O2 concentration <5%), all strains showed lower MLC to MTZ, TNZ and ONZ than >100 microgram/ mL (aerobic resistance cut-point proposed by M ller etc.). MLC of doxycycline ranged 62.5 to 250 microgram/mL both in microaerobic and anaerobic conditions. All strains of T. vaginalis growed well in 3,000 microgram/mL of povidone-iodine. 22 strains (84.6%) among 26 T. vaginalis strains showed MLCs of 3.5 mM~7.0 mM to zinc sulfate. Gentian violet showed 15.6~62.5 microgram/mL of MLC. CONCLUSION: In absolute anaerobic culture, 4 strains (15.4%) among 26 T. vaginalis strains were resistant to metronidazole. But these 4 strains were not resistant in microaerobic culture depending on Miler's aerobic resistance cut-point (>50~100 microgram/mL), the value decided in normal O2 pressure. Vaginal PO2 is 0~28mm Hg (median 1 mmHg) at healthy or trichomonas-infected women. Therefore, we think that his aerobic resistance cut-point value is hard to be available in microaerobic condition and microaerobic resistance guide-line is to be established newly.