Greenshell (Perna canaliculus) and Blue (Mytilus galloprovincialis) mussels were experimentally contaminated with yessotoxin (YTX) by feeding with a culture of the dinoflagellate Protoceratium reticulatum. Tissue localization of YTX and its derivatives was measured by HPLC- FD and their disappearance from the shellfish was monitored over a 10 day depuration period. After feeding, only YTX could be detected in Greenshell mussels whereas in Blue mussels 45-hydroxy yessotoxin (45- OH-YTX) was the predominant molecular species observed, comprising >90% of the total toxin present. Neither derivative could be detected in tissues other than the digestive gland. The slow rate of disappearance of YTX from Greenshell mussel digestive glands over time (0.06 µg YTX g-1 day-1 ) was comparable with the rates observed in naturally contaminated shellfish (0.04 µg YTX g-1 day-1 ). The rate of disappearance of 45-OH-YTX from Blue mussels was possibly more rapid though wide variation between replicates made this uncertain. This experiment clearly demonstrates that different bivalve species may interact with dinoflagellate polyether toxins in different ways.