AbstractThe composition of eight samples of commercial copaiba oils, used in the Amazonian region as antiinflammatory agents and available in popular markets, were analysed by gas chromatography/mass spectrometry (HRGC‐MS). Major differences were observed in their chemical composition and some adulterations were pointed out. When tested in vivo oils 1 and 3, and to a lesser extent oil 6, significantly inhibited bradykinin‐induced oedema formation. The other tested oils had no effect. When assessed in carrageenan‐induced oedema formation, oils 1, 2 and 6, but not oil 3, significantly attenuated the oedema formation. The other tested oils failed to affect carrageenan‐induced paw oedema. Oils 1 and 6 were further fractionated and several sesquiterpenes and diterpenes were detected. It is suggested that the naturally occurring sesquiterpenes present in the copaiba oils seem to be responsible for the antiinflammatory action reported in the folk medicine. Furthermore, our results clearly show an adulteration in copaiba oils available in Brazil. Copyright © 2001 John Wiley & Sons, Ltd.