abstract essential oils of fresh plant parts of bidens pilosa var. minor (bl.), bidens alba (l.) dc. (tribus heliantheae, asteraceae) and flaveria linearis lag. (tribus helenieae, asteraceae) were obtained by hydrodistillation and analyzed by gc, gc/ms and hplc. forty-three compounds were identified in the oils of b. pilosa var. minor and b. alba, which represents 83-94 % of the total components detected. qualitatively, the compositions of the two oils were similar. in addition to the usual terpenes (-pinene, -caryophyllene, -copaene, germacrene d), three polyacetylenic compound were identified in the oils of each species. in the aerial parts of both b. pilosa and b. alba, 1-phenylhepta-1,3,5-triyne (pht) was the most abundant component of the oils (30-50%). the other two polyacetylenes were 1-phenylhept-5-ena-1, 3-diyne and 7-phenylhept-2-ena-4,6-diynyl acetate. the latter, which was absent in flower and leaf oils, was predominant in the root oils of both plants. the root oil of b. alba also contained three eugenol derivatives that together accounted for more than 20% of the oil. two could be identified as eugenol isobutyrate and 1'-isobutyryloxy-eugenol isobutyrate. thirty components were identified from the different plant parts of flaveria linearis lag. this represented 92-94% of the total components of the oil. the oils from the aerial organs of f. linearis were mainly composed of terpenes (-pinene, myrcene, limonene, (e)--ocimene); however, 2-(but-3-en-1-ynyl)-5-(penta-1,3-diyn-1-yl)-thiophene was also an abundant component of the oils from both the flowers and the leaves. in contrast, the root oil of f. linearis consisted mainly of thiophenes. four thiophenes were identifed: 5-(but-3-en-1-ynyl)-2,2'-bithiophene and 2,2'-5',2''-terthiophene, were major constituents. 2-(but-3-en-1-ynyl)-5-(penta-1,3-diyn-1-yl)-thiophene and 5'-methyl-5-(but-3-en-1-ynyl)-2,2'-bithiophene, were minor components of the root oil.