Abstract: A paralytic food poisoning incident due to ingestion of the goby Yongeichthys nebulosus occurred in Shinchu County, Taiwan , in June 1995 . The couple poisoned had symptoms which were marked by severe numbness of the lips, vomiting and impaired breathing. Three uneaten fish specimens were dissected into muscle, head and viscera, and analyzed for toxicity. Using a tetrodotoxin bioassay the fish showed the highest toxicity of 24, 120 and 84 mouse units per gram (MU/g) in muscle, head and viscera tissues, respectively. The fish toxin was combined and purified by Diaflo YM-1 membrane ultrafiltration and Bio-Gel P-2 chromatography. The analyses of purified toxin by electrophoresis, high performance liquid chromatography and gas chromatography-mass spectroscopy indicated that the causative toxic agents were tetrodotoxin and a related substance anhydrotetrodotoxin.