Abstract : Numerous assessment tools based on biological units (i.e. bioassays) have been developed to complement physicochemical or immunochemical methods. Bioassays provide complex information on the overall toxic potencies or biological activities of cyanobacterial samples including isolated cyanotoxins as well as natural blooms. The present chapter provides rationale beyond the use of bioassays and shows key examples for the assessment of toxic cyanobacteria covering both the toxicology (or more specifically toxinology for natural toxins) and ecotoxicology arenas for all levels of biological organization (from in vitro to in vivo, from plants to animals). At the present time, bioassays for potential use in routine monitoring need further research and validation, and there is no clear agreement among scientists on the list of recommended bioassays. Nevertheless, bioassays play an important role in the primary screening of cyanobacteria for toxic compounds and for their detection under specific situations such as limited access to advanced instrumental analytical equipment or indications of toxic metabolites other than (or in addition to) the known cyanotoxins.
