Citrus flavonoids are dietary antioxidants that may protect against oxidative stress linked to inflammation and reduce the risk of macromolecule damage caused by free radicals. Three citrus flavonoids – naringin, naringenin and hesperidin – have been examined for their ability to activate caspase-3, a marker of apoptosis execution, in human polymorphonuclear neutrophilsin vitro, stimulated and non-stimulated with phorbol 12-myristate 13-acetate. The flavonoid potency to reduce reactive oxygen species generation was also assessed in measurements of superoxide radical and luminol dependent chemiluminescence. The caspase-3 activity depended on the time of flavonoid treatment and was increased markedly in phorbol-treated cells incubated with flavonoids for 24 h. Hesperidin at a concentration of 100 μm exerted the strongest stimulating effect on the enzyme (137% of control). Flavonoids inhibited the neutrophil ability to generate superoxide radical and 10–100 μm hesperidin appeared the most active phytochemical. The antioxidant capacity of the examined flavonoids was most prominently expressed in the chemiluminescent measurements. The obtained results suggest that reactive oxygen species may inhibit apoptosis via caspase-3 inhibition and the antioxidant action of citrus flavonoids may reverse this process. Copyright © 2008 John Wiley & Sons, Ltd.