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The rare diarrhetic shellfish toxin, dinophysistoxin-2 (DTX-2), was isolated from the digestive glands of mussels (Mytilus edulis). This was achieved by chromatography on silica and Sephadex LH-20 followed by reversed-phase solid phase extraction and semi-preparative high-performance liquid chromatography (HPLC) with an Ultremex C18 column. Using 1-bromoacetylpyrene (BAP), as a precolumn derivatisation reagent, the diarrhetic shellfish toxins, okadaic acid (OA), dinophysistoxin-1 (DTX-1) and DTX-2, were determined by HPLC with fluorimetric detection. Derivatisation using BAP was compared with 9-anthryldiazomethane (ADAM) and, although the latter exhibited a four-fold better sensitivity, the BAP method gave fewer artefact peaks from reagent decomposition. The limits of detection of OA and DTX-2 were 0.4 ng on-column using BAP, which permits this method to be used for the regulatory control of these toxins in shellfish.