Domoic acid is a neurotoxin produced by marine diatoms. This toxin can be accumulated through the marine food chain, mainly by filtering mussels, and intoxicate human consumers. This paper reports the settings to determine the presence of domoic acid in mussel tissue by reversed phase liquid chromatography with diode array detection (HPLC-DAD) and the results of analysis of samples from mussel culture In the coast of Santa Catarina. Thirty samples were taken between 31 of August of 1998 and 26 of February of 1999 from Armação do Itapocoroy bight and other culturing areas. Although species from Pseudo-nitszchia, a potentially toxin producer diatom, are highly abundant at the water column, until the present no toxin has been found in mussels.