Abstract: Attempts were made to elucidate the responsible toxins in the gastropod Niotha clathrata and Zeuxis scalaris which recently caused food poisoning incidents inSouth Taiwan. The remained (cooked) and captured (live) specimens of both gastropods were assayed for toxicity (as tetrodotoxin=TTX). The average toxicity of cooked and live specimens was 150±126 (mean±S. D.) and 345±192 mouse unit (MU) in N. clathrata, and 13±9 and 98±46 MU in Z. scalaris, respectively. The toxin was partially purified from the methanolic extract of the gastropod by ultrafiltration and Bio-Gel P-2 column chromatography. Cellulose acetate membrane electrophoresis, TLC, and HPLC analyses demonstrated that the toxin consisted mainlyof TTX (about 80%), along with minor paralytic shellfish poison (PSP, about 20%). The PSP components were identified as gonyautoxin 1-4 and neosaxitoxin in bothgastr-opods. It was concluded from these results that the causative agents of theabove food poisoning were TTX and PSP.