The composition of volatile oils produced byEuphorbia fragifera is reported. The plant samples were collected in two different habitats on the Karst plateau North of Trieste (North Eastern Italy). The analysis was performed by capillary GC. Differences between samples from the two habitats have been found in the quantitative composition of the oils. The plants coming from the optimal, xeric habitat produce oils in which aromatic terpenes (mostly carvacrol) are more abundant, whereas the oils of plants growing in shady and moist sites are mostly composed by acyclic compounds (chiefly geraniol). It seems therefore possible to distinguish two chemical variants ofEuphorbia fragifera. The number and kind of pollinating insects have been recorded. Terpenoids from the two kinds of essential oil could be responsible of two different pheromones that attract different kinds of pollinators.