Five strains of Trichomonas vaginalis were independently inoculated into Cysteine-Peptone-Liver infusion-Maltose medium (CPLM medium), and gases in the culture bottle were qualitatively analysed at five days after the inoculation by gas chromatography mass spectrometry (GC-MS). Methane, ethane and carbon dioxide were commonly found in the gases produced during the culture of Trichomonas vaginalis in vitro. Carbon monoxide was also found in the gases from 4 of 5 strains. Small amount of both ethylene and propane was also noted in 3 of 5 strains. These gaseous molecules were supposed to be produced by Trichomonas vaginalis in vitro, presumably by the catabolism of amino acids. It was also suggested that these gases, including methane, ethane, carbon dioxide, carbon monoxide, ethylene and propane, were responsible for the foamy discharge found in the vagina of patients with Trichomonas vaginalis.