The cyclic imines group includes gymnodimine, spirolides, pinnatoxins, prorocentrolide and spirocentrimine. The presence of this group of compounds in shellfish was discovered because of their very high acute toxicity in mice upon i.p. injections of lipophilic extracts. When present at elevated levels, they rapidly kill mice, and their presence may interfere with the MBA for OA, BTXs, and AZA groups. At sublethal doses, the mice recover rapidly. The toxic potential of the cyclic imines is much lower via the oral route. The regulatory significance of the cyclic imine toxins is still unclear. Although gymnodimine and spirolides are now known to commonly occur in microalgae and/or bivalve molluscs from several parts of the world (Canada, Denmark, New Zealand, Norway, Tunisia, the United Kingdom of Great Britain and Northern Ireland, and the United States of America), there have been no reports of adverse effects in humans.