The chemical composition of the essential oils from the needles of Pinus ponderosa (north american pine), P. resinosa (red pine) and P. strobus (eastern white pine) has been determined by GC/MS (FID). The essential oils from P. resinosa and P. ponderosa in comparison to P. strobus have been characterized by the higher content of β-pinene (42.4%, 45.7% and 7.9% respectively). On the other hand, α-pinene (17.7%) and germacrene D (12.2%) were dominant compounds of P. strobus. Moreover the essential oil from P. resinosa was more rich in myrcene-15.9%. Estragole and Δ-3-carene, each one in amount ca 8% were identified only in P. ponderosa. The content of essential oils in the needles slightly varied - 0.65% - P. resinosa, 0.4% - P. strobus, 0.3% - P. ponderosa. The antifungal activity has been investigated towards Fusarium culmorum, F. solani and F. poae. The strongest activity was observed for the essential oil from P. ponderosa, which fully inhibited the growth of fungi at the following concentrations - F. culmorum, F. solani at 2% and F. poae at 5%.

In the framework of the correlation between chemotaxonomy and chemical analysis studies, the chemical composition of the essential oils of four varieties of Thuja species cultivated in Poland − T. occidentalis ‘globosa’, T. occidentalis ‘aurea’, T. plicata and T. plicata ‘gracialis’ − were investigated by GC and GC-MS. Thirty-one compounds were identified from T. occidentalis ‘globosa’, representing 96.92% of the total oil; twenty-seven from T. occidentalis ‘aurea’ (94.34%); thirty-one from T. plicata (94.75%); and thirty compounds from T. plicata ‘gracialis’ (96.36%). The main constituents in all samples were the monoterpene ketones α- and β-thujone, fenchone and sabinene, as well as the diterpenes beyerene and rimuene.The chemosystematic value of the total ketone content of all samples (which varied from 54.30–69.18%) has been discussed and investigated. The constituents, beyerene and the mixture of α- and β-thujone, were isolated from the oils and tested against six Gram-positive and -negative bacteria and three pathogenic fungi. The oils of the two T. plicata species exhibited significant antimicrobial activity, while the mixture of α- and β-thujone showed very strong activity as well.