Microcystins are potent hepatotoxins produced by several genera of aquatic cyanobacteria (blue-green algae).Due to the worldwide distribution of these cyanobacteria, the occurrence of microcystins has been reported on every continent.This class of algal toxins has repeatedly caused poisoning of domestic and wild animals, as well as human fatalities.Their tumour promoting potential is another important aspect of their toxicological profile.Long term exposure (e.g.via drinking water) at low dosage levels might cause liver cancer, even if symptoms of acute toxic effects are not seen.High concentrations of microcystins can be found especially in water bodies affected by mass proliferation of cyanobacteria, so-called algal blooms.