The chemical composition and spasmolytic activity in isolated guinea-pig ileum of the essential oil ofArtemisia albaTurra has been determined. The oil was hydrodistilled from the plant's flowering tops gathered in two very ecologically different Appennine environments: die gravely substrata of the mean-water bed of the Taro river (Taro-oil)and the calcareous-marly declivities of a modest relief of the central Apennines (Morro di Camerino,Morro-oil). GC and GC/MS analyses of the oil revealed a similar qualitative composition (terpenes and phenols for a total of 59 components identified) with a constant predominance of thujone and camphor in theTaro-oiland a percentage of artemisia ketone in theMorro-oilwhich varied notably in the two harvests gathered in successive years. All the samples demonstratedin vitro(against carbachol) a notable dose-dependent, essentially non-competitive spasmolytic action which was greatest in the sample with the highest content of artemisia ketone.