Abstract The essential oil compositions of the upper parts of six Lomatium species, Lomatium brandegei, Lomatium eastwoodiae, Lomatium graveolens, Lomatium howelii, Lomatium junceum and Lomatium parryi, were determined by comparing the reported GC, GC/MS data of the oil components as well as by comparing the GC/MS retention times and the mass spectra of several other components with authentic samples. The Indra swallowtail Butterfly has been observed to lay eggs on these Lomatium species. A principal component analysis of the essential oil composition of the six species against the essential oil of Lomatium dissectum var. multifidum, a non-Indra swallowtail Butterfly host, was conducted.