A rapid HPLC method with fluorescence detection of pectenotoxin-2 (PTX2), a polyether macrolide toxin, in microalgae is presented. A dienophile reagent, DMEQ-TAD, was used for precolumn fluorescence labeling. PTX2 could be quantitatively detected in the range 1–200 ng. This method confirmed the occurrence of PTX2 in net haul samples mostly composed of dinoflagellates Dinophysis spp. collected in the Adriatic Sea, Italy and Mutsu Bay, Japan. Copyright © 1999 John Wiley & Sons, Ltd.