Human intoxications, following the consumption of Irish mussels (M. edulis), have occurred in The Netherlands (1995), Arranmore Island (1997), France (1998) and Italy (1998). The contaminated shellfish were cultivated in four different regions encompassing the entire west coast of Ireland. These intoxications have now all been attributed to a new family of shellfish toxins. Three toxins have been isolated and structurally elucidated and they contain a novel spiro ring assembly. The major toxin, has been named azaspiracid (AZ-1) but substantial amounts of its methyl and demethyl analogues, AZ-2 and AZ-3, respectively, were also present in shellfish. The aetiology of azaspiracids and toxin dynamics in shellfish have been studied using liquid chromatography-mass spectrometry methods, especially LC-MS^3, and strong evidence has been obtained that azaspiracids are produced by a dinoflagellate. Azaspiracids are persistent in shellfish and have been found in mussels as long as eight months after the initial intoxication. In several instances, toxin levels in oysters (C. gigas ) have been comparable to the levels found in mussels from the same cultivation area. These toxins have also recently been identified in mussels from England and Norway which implies a more widespread intoxication of European shellfish than has previously been appreciated. In animal tests, azaspiracids show pronounced neurotoxic effects and produce severe damage to the intestine, spleen and liver tissues. Since azaspiracids are toxicologically and chemically different from previously identified groups of shellfish toxins, a new toxic syndrome has been declared and named, azaspiracid poisoning (AZP).