Ethanol extract of propolis (EEP), a natural beehive product, has been known for centuries for a variety of beneficial traditional medical properties, among which an anti-inflammatory effect is a major one. Now that most of its components have been isolated and recently identified, we tested 19 of them (all phenolic compounds) for their degree of anti-inflammatory activity. This was performed by evaluating the luminol-enhanced chemiluminescence, formed after their scavenging free radicals, generated by neutrophils that had been stimulated by phorbol myristate acetate. Caffeic-acid-phenylethyl-ester abolished the chemiluminescence completely at a concentration of 10 microM, while three flavone derivatives and three flavonols (galangin, kaempferol and kaempferid) diminished this chemiluminescence by 73-93% at the same concentration. These results indicate that some of the phenolic components of the ethanol extract of propolis are its active components in exerting its renowned anti-inflammatory activity.