The polysaccharolytic enzymes of the abalone Haliotis midae and its resident gut bacteria were investigated. Bacteria isolated from the abalone gut were able to degrade the polysaccharides laminatin, carboxymethylcellulose (CMC), alginate, agarose and carrageenan. Detection of alginate lyase, CMCase, laminarinase, agarase and carrageenase in the hepatopancreas, which was devoid of bacteria, indicated that H. midae produces a range of polysaccharases. The endogenous polysaccharases of abalone fed either Ecklonia maxima or Gracilaria verrucosa varied in response to diet. It is proposed that bacteria resident in the digestive system of H. midae assist in the digestion of alginate, laminarin, agarose, carrageenan and cellulose.