As intestinal metabolism strongly influences the bioavailability of flavonoids, this study investigated the microbial deconjugation and degradation of the most common flavan-3-ols using the pig cecum in vitro model system developed in the authors' group. The microbial degradation of (+)-/(-)-catechin, (-)-epicatechin, (-)-gallocatechin, (-)-epigallocatechin, (-)-gallocatechin gallate, (-)-epigallocatechin gallate, procyanidin B2, and gallic acid was investigated under anaerobic physiological conditions in single incubation experiments and as a mixture. Incubation was done with the microbiota from three different animals in repeat determinations (n = 6). The flavan-3-ols under study were almost completely metabolized by the intestinal microbiota within 4-8 h. No difference was observed for catechin enantiomers. In addition to monomeric flavonoids, procyanidins are also metabolized by the intestinal microbiota as shown for procyanidin B2. The arising hydroxylated phenolcarboxylic acids are similar for all tested substances. These small phenolic degradation products might be responsible for the observed antioxidative activities described in the literature.