The Achillea millefolium complex is a group of taxonomically hardly separable species. Yarrow has the tendency to hybridize and to vary in phenotype. An obvious characterization of the species or hybrids is not just important for the taxonomical distinction but also for a reliable assessment of herbal drug quality. Most of the Achillea plants are still gathered from natural populations. According to the variation in phenotype, mixtures with Achillea species, which contain allergy setting compounds, often cannot be determined. Morphometric investigations exclusively do not replace a further chemical characterization. Therefore we tried to assess the composition of the chiral monoterpenes alpha-pinene, beta-pinene and sabinene. They were selected because of their frequency in the essential oil of Achillea species. By method of M.C.S.S. (Moving Capillary Stream Switching) the differentiation of stereoisomeres succeeded directly from the essential oil, which was distilled or extracted by headspace trapping at room temperature. The enantiomeric distribution neither depends on the method of extraction, nor on the habitat or the developmental stage of Yarrow. Since the compositions of enantiomeres from several Achillea species and their hybrides are of different pattern, it seemed to represent an additional marker. Though investigations of all species within the Achillea millefolium group and possibly of further chiral compounds are necessary to ensure these results.