Out of the circa 5000 microalgae known, around 100 marine species of unicellular algae have been shown to produce several hundred biotoxins worldwide. Such biotoxins may be harmful to man through consumption of fish and shellfish exposed to such algae or through direct contact. Many official methods aimed at the detection of such toxins had traditionally been based on biological assays, due to the lack of reference compounds. Recently, legislation for shellfish safety in Europe introduced targeted MS screening for lipophilic toxins. Due to globalization of trade and climate change, there is a need to develop methods for untargeted screening to fully protect consumer safety, e.g. LC-HRMS. For this purpose we studied the metabolomes of marine microalgae using HRMS techniques