The diarrhetic shellfish toxins, okadaic acid (OA) and dinophysistoxin 1 (DTX1), are polyeters produced by some species of the Dinophysis and Prorocentrum genera. These toxins can accumulate into the mussel tissues and later intoxicate human consumers. The production of AO and DTX1 by Prorocentrum micans Ehrenberg 1833 and P. obtusum Ostenfeld 1908, two especies isolated from a mussel culture area, was investigated by the pre-column derivatization HPLC-FLD method. Results showed that these two dinoflagellate do not produce AO or DTX1 and they can be ruled out from the potentially toxin producing algae roll find in the mussel culture area.