Extracts of feverfew inhibit secretion of granular contents from platelets and neutrophils and this may be relevant to the therapeutic value of feverfew in migraine and other conditions. In this investigation we fractionated an extract of feverfew and obtained eleven fractions with antisecretory activity. The activity. The active fractions, together with two fractions that were devoid of anti-secretory activity, were examined using 1H NMR and infrared spectroscopy. All the active fractions (but neither of the inactive fractions) contained compounds with an alpha-methylene butyrolactone unit. Five compounds that contain this unit were identified as parthenolide, 3-beta-hydroxyparthenolide, secotanapartholide A, canin and artecanin, all of which are sesquiterpene lactones. It is very likely that these and other sesquiterpene lactones that contain an alpha-methylene butyrolactone unit are responsible for the anti-secretory activity in extracts of feverfew.