The New Zealand green-lipped mussel (Perna canaliculus) is the source of a para-pharmaceutical called Seatone. Claims have been made that the preparation may be helpful in the management of inflammatory joint disease but results of clinical studies to date have been contradictory. An earlier experimental study demonstrated anti-inflammatory activity in the crude preparation and further experiments to isolate and characterise the active fraction were indicated. A two-step fractionation procedure resulted in an extract, which although only 16 percent by weight of the parent material, retained anti-inflammatory activity. Experiments involving alternative routes of administration, with heat or enzyme treatment of the active extract and a comparative analysis of fractions from related bivalves, all demonstrated that the anti-inflammatory effect was genuine and did not result from counter-irritancy. The initial results suggest that the active agent is a proteinaceous macromolecule.