essential oils obtained by hydrodistillation from leaves of mentha pulegium l. and mentha rotundifolia (l.) huds. from uruguay were analysed by gc-fid and gc-ms. oxygen-containing monoterpenes were the main group of constituents in both oils. pulegone, isomenthone and menthone were the major components in the oil of m. pulegium, whereas piperitenone oxide and (z)-sabinene hydrate were the major ones in m. rotundifolia. enantiomerically pure (-)-menthone, (+)-isomenthone, (+)-isomenthol, (-)-menthol and (+)-pulegone were detected by multidimensional gas chromatography in the case of m. pulegium oil.