The inhibitory properties of procyanidins (a standardized oligomeric catechin fraction) from Vitis vinifera L. seeds on the respiratory burst and on the release of granule components myeloperoxidase, beta-glucuronidase and elastase were studied in activated human neutrophils. Procyanidins strongly inhibit superoxide generation with an IC(50) of 7.2 microM, through a direct scavenging of superoxide and prevent the release from calcium ionophore activated neutrophils of beta-glucuronidase (IC(50) = 13.9 microM), myeloperoxidase (IC(50) = 7.2 microM) and elastase (IC(50) = 5.4 microM). In addition they dose-dependently inhibit the activity of myeloperoxidase released from calcium ionophore-stimulated cells with an IC(50) value of 2 microM. The monomeric constitutive unit (+)-catechin was far less active than procyanidins in all the models tested. These results evidence that procyanidins efficiently restrain the inflammatory response of activated neutrophils in vitro and whenever absorbed in vivo can prevent their oxidative discharge at the site(s) of their adhesion.