the essential oils from two members of the asteraceae ( acanthospermum hispidum dc. aerial parts, and leaves of tithonia diversifolia (hemsley) a. gray), growing wild in osun state, nigeria, have been characterised by combined gas chromatography (gc) and gas chromatography-mass spectrometry (gc-ms) analyses. twenty-nine components have been fully identified and grouped into monoterpene hydrocarbons (22.2%), oxygenated monoterpenes (4.6%), sesquiterpenes hydrocarbons (58.2%) and oxygenated sesquiterpenes (10.8%) in a. hispidum. the main constituents of the oil were -caryophyllene (28.0%), -pinene (15.9%) and bicyclogermacrene (11.0%) among the hydrocarbon compounds, and bisabolol (8.9%) and carvacrol methyl ether (4.1%) among the oxygenated components. tithonia diversifolia essential oil comprised seventeen components and was characterised by a predominant content of monoterpene hydrocarbons (87.9%), cis--ocimene (43.7%), -pinene (28.6%) and limonene (12.0%) being the main compounds. sesquiterpenes represented ca. 10% oil, as sum of hydrocarbons and oxygenated components. a new chemotype is established for t. diversifolia, while the nigerian a. hispidum is being reported for the first time as a new source of essential oil with some distinction in composition from those of other sources.