In vitro effects of catechins and their oligomers linked by C4 --> C8 bonds are major antioxidative components of chocolate and cocoa. Their effects on the susceptibility of human low-density lipoprotein (LDL) to oxidation were evaluated. The strength of the antioxidative activity was measured using copper ions as the radical generator as compared by weight varied in the following order: (+)-catechin > procyanidin B2 > or = (-)-epicatechin > or = procyanidin C1 > cinnamtannin A2. Using 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) (MeO-AMVN) as the radical generator, the order was (-)-epicatechin > or = procyanidin B2 > or = procyanidin C1 > (+)-catechin > or = cinnamtannin A2. It is suggested that these compounds contribute to the activity of cacao products to protect LDL from oxidation.