Paralytic shellfish poisoning (PSP) is caused by consumption of a wide variety of shellfish which accumulated saxitoxins (STXs) from marine dinoflagellates (Alexandrium minutum, A. tamarense, Gymnodinium catenatum, Pyrodinium bahamense) and affect a wide variety of shellfish. There are about 20 saxitoxin analogs with closely related structures. A regulatory level of 0.8 mg/kg shellfish meat as STX equivalents has existed in North America and Europe for many years. The methods of determination of saxitoxins are reviewed: biological assays in vivo and in vitro, biochemical and chemical assays. The mouse bioassay protocol has been widely used and has protected public health for over 50 years using an action level of 0.8 mg/kg STX.2HCL equiv. It is a routine method, and in EU it is the reference method if the results are challenged (Commission Regulation 2005/274/CE). However ethical issues, relating to the use of live animals, affect the acceptance and use of mouse bioassay in some countries. A precolumn-derivatization liquid chromatography method (Lawrence method) is approved as European Norm by CEN and by AOAC as official method of analysis. Others techniques such as receptor binding assay (in vitro bioassay), immunoassay (commercial test kits) and postcolumn-derivatization liquid chromatography can be used as alternative method for routine monitoring. Capillary electrophoresis and liquid chromatography with mass spectroscopic detection are studied in research laboratories.