This European Prestandard specifies a method for the quantitative determination of saxitoxin (STX), dc-saxitoxin (dc-STX) and the qualitative determination of neo-saxitoxin, and the gonyautoxins GTX-2 and GTX-3 in mussels. The method can also be used to identify the N-sulfocarbamoyl toxins C-1, C-2, GTX-5 and GTX-6 after hydrolysis and, if these toxins are present, to exclude false positive results for GTX-2, GTX-3, neo-saxitoxin and saxitoxin. For mussel the limit of quantification is for saxitoxin 0,04 mg/kg mussel meat and for dc-saxitoxin 0,03 mg/kg mussel meat (signal/noise = 10). The limits of detection for C-1, C-2, GTX-2, GTX-3, GTX-5, GTX-6 and neo-saxitoxin have not been determined.