Previous laboratory based investigations of a commercially prepared freeze-dried extract of the NZ green-lipped mussel (Perna canaliculus) showed that the material had the capacity to inhibit experimentally induced inflammation. The activity was thought to reside within an aqueous fraction containing high molecular weight material, possibly a polysaccharide. In the present study, a polysaccharide (glycogen) has been extracted from Perna canaliculus and its anti-inflammatory activity examined in an attempt to characterise further the high molecular weight components of this mollusc. Glycogen extracts administered i.v. demonstrated a dose-dependent anti-inflammatory effect in rats with carrageenin-induced footpad oedema. Mobilisation of neutrophils to the site of an inflammatory stimulus was also significantly reduced. This activity was lost if the glycogen extract was treated with KOH or proteinase K, suggesting that the anti-inflammatory properties resided within a protein moiety associated with the glycogen.