Bacteroides thetaiotaomicron NCTC 10582 grown in media containing pig gastric mucin was found to be capable of producing all the glycosidases required to degrade the carbohydrate moieties of human colonic mucin. These are α-fucosidase, β-galactosidase, α-N-acetylgalactosaminidase, β-N-acetylglucosaminidase and neuraminidase. Moreover, a novel glycosulphatase was identified using glucose-6-sulphate as substrate. This enzyme has a Km of 43·4 mmol/l and a pH optimum of 5·0. The bacteria, when cultured for 24 h in broth, were capable of removing 18% of [35S]-sulphate from [35S]-labelled mucin and of removing 15% of [3H]-glucosamine from [3H]-glucosamine-labelled human colonic mucin. The results suggest that this bacterium is likely to play an important role in mucus degradation in the human colon.