abstract the leaf oils of the two australian species of decaspermum have been examined by gc and gc/ms. the leaf oil of d. struckoilicum contained -pinene (37.5%) as its principal component in an oil that contained similar amounts of mono- and sesquiterpenes. the major sesquiterpenes identified in the oil were -caryophyllene (2.4%), -humulene (2.2%) and - and -eudesmol (8.2% and 8.1%, respectively). decaspermum humile produced a leaf oil that contained either approximately equal amounts of mono- and sesquiterpenes or had a majority of the latter components. the principal monoterpenes were a-thujene (0.1-13%) and -pinene (0.2-21%). other prominent monoterpenes identified were limonene (0.2-8%), myrcene (0.3-10%), -phellandrene (0.1-5%), linalool (0.3-9%) and terpinen-4-ol (0.3-6%). 1,8-cineole was usually absent from the oils. the main sesquiterpenes identified in the oils were -caryophyllene (0.7-5%), aromadendrene (1-6%), viridiflorene (1-7%), -cadinene (0.4-14%), bicyclogermacrene (0.2-10%), globulol (1-9%) and in some collections 7-epi--selinene (trace-9%). key word index: decaspermum humile decaspermum struckoilicum myrtaceaeessential oil composition-thujene-pinenebicyclogermacrene-cadinene