abstract the composition of secondary metabolites is often modified by environment and ontogenesis. to explicitly study the influence of temperature on essential oil compositions, experiments on a hybrid of origanum vulgare x origanum majorana (containing both major monoterpene pathways of the genus origanum, 'sabinyl' and 'cymyl'-pathway) and on origanum syriacum ssp. syriacum (only 'cymyl'-pathway) were conducted in growth chambers. clonally propagated plants were grown at three different temperature levels and the solvent extracts analyzed by gc/ms for their composition of essential oil compounds. the major 'sabinyl' compound cis-sabinene hydrate was not influenced by temperature, while temperature significantly influenced thymol and carvacrol and other essential oil compounds. although thymol and carvacrol are closely related monoterpene phenols, they reacted to varying levels of temperature in an opposite way. thymol increased with decreasing temperatures while carvacrol increased with increasing temperatures.