the yield and composition of essential oils from leaves, stems, umbel rays and also from whole aerial parts of bupleurum gibraltarium lam. (apiaceae) were determined during the pre-flowering, full flowering, late flowering, and fruiting vegetative periods. a fruit sample was also studied for comparative purposes. leaves (0.8-1.8% yield) and stems (0.3-0.7%) reached their maximum oil content during the late flowering period, whereas umbel rays (2.2-3.7%) reached it in full flowering. oil samples were analyzed by capillary gc and gc/ms components which were found in amounts greater than 2% were selected to carry out a seasonal study. in the leaf oils, sabinene (12.0-33.9%) and limonene (7.8-23.4%) were the main components, the sabinene level being minimum in full flowering and maximum in fruiting. in stem oils, sabinene (4.7-21.6%) and 2,3,4-trimethylbenzaldehyde (9.3-13.6%) were the main components, the sabinene level being minimum in pre-flowering and maximum in full flowering. in umbel ray oils, sabinene (20.7-43.1%) was the first component in all the phenological periods, followed by -pinene (7.3-28.2%). both monoterpenes increased their levels in late flowering and reached minimum amounts in fruiting. (c) 2006, taylor & francis group, llc. all rights reserved.