Epicatechin 3-O-gallate and various procyanidins obtained from grape seeds were tested for their scavenger capacity for superoxide radical (O2.-) and hydroxyl radical (.OH) in aqueous models. Quantification of O2.- and .OH scavenger capacities was carried out, respectively, by polarography and by the extent of deoxyribose degradation. All the compounds assayed are potent scavengers of these radicals compared to trolox (for D2.-) and ethanol and mannitol (for .OH). Catechin monomers are also potent scavengers, especially of .OH. Gallic acid esterification increased the O2.- and .OH scavenger capacity of the dimer procyanidins. However, esterification position was also important. A difference in the O2.- scavenger capacity was noted between dimers having a C4-C6 and C4-C8 linkage. Procyanidin B2 3'-O-gallate was found to be the most effective compound in trapping oxygen free radicals.