abstract the oil of peppermint (mentha x piperita l.) from the usa, a dementholized cornmint oil (m. canadensis l.), and a fraction of the dementholized cornmint oil were analyzed by gc-fid and gc/ms. the main constituents of the three samples analyzed were menthone (23.4%, 20.4% and 58.3%, respectively) and menthol (40.7%, 41.2% and 12.3%, respectively). the two oils, the cornmint oil fraction and seven mint oil compounds [(-)-menthol, (-)-menthone, (+/-)-menthyl acetate, 1,8-cineole, limonene, -pinene and -caryophyllene] were investigated for their antimicrobial effects against two gram-positive bacteria (staphylococcus aureus and enterococcus faecalis), five gram-negative bacteria (escherichia coli, pseudomonas aeruginosa, proteus vulgaris, klebsiella pneumoniae and salmonella sp.) and the yeast candida albicans using a modifed agar dilution and agar diffusion method. medium to high antimicrobial effects were found for both oils, the dementholized cornmint oil fraction, and the target-compounds against all gram-positive bacteria, whereas against the gram-negative bacteria and the yeast, one or more samples showed only weak or no activity.