Azaspiracids have recently been identified as the toxins responsible for a series of human intoxications in Europe since 1995, following the consumption of cultured mussels (Mytilus edulis) from the west coast of Ireland. Liquid chromatography-mass spectrometric (LC-MS) methods have been applied in the study reported here to investigate the new human toxic syndrome, azaspiracid poisoning. Separation of azaspiracid (AZA1) and its analogues, 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3), was achieved using reversed-phase LC and coupled, via an electrospray ionisation source, to an ion-trap mass spectrometer. These azaspiracids have now been identified in mussels from Craster (north-east England) and Sognefjord (south-west Norway) using source collision induced dissociation-MS and multiple tandem MS detection. AZA1 was the predominant toxin and toxin profiles were similar to those found in contaminated Irish shellfish. This is the first report of the occurrence of these azaspiracids outside Ireland with the significant implications that these toxins may occur in shellfish throughout northern Europe.