Substituted (hydroxy-, epoxy- and dicarboxy) fatty acids have been analyzed in the needles of two gymnosperms (Pinus sylvestris andJuniperus communis) and the leaves of four angiosperms (Betula verrucosa, Populus nigra, Quercus petraea andCorylus avellana) growing in the Lake Léman basin. The differences in the distributions of the acids that have been analyzed are greater between the various species than between the spring and autumn samples of a given species. Moreover, the isomeric composition of the 8,16-, 9,16- and 10,16-dihy-droxypalmitic acid mixture is specific for each species.