Polyunsaturated alkamides isolated from Achillea species, Echinacea angustifolia DC., Anacyclus pyrethrum (L.) Link, and Aaronsohnia pubescens (Desf.) Bremer & Humphries, (Compositae) were shown to possess inhibitory activity in in vitro cyclooxygenase (sheep seminal microsomes) and 5-lipoxygenase (porcine leukocytes) assays. Activity appeared to depend on the particular structure of the alkamides.