Food poisoning due to ingestion of two fishes, Yongeichthys nebulosus and Sillago japonica, occurred in Kaohsiung, Taiwan, in February 1997. Two male persons (48 and 58 years old) were poisoned, with symptoms featured by dizziness, nausea, vomiting, numbness, and difficulty in respiration. All of the specimens of fish retained by the victims were combined and consisted of Yongeichthys nebulosus and Sillago japonica. These retained specimens were assayed for anatomical distribution of toxicity (as tetrodotoxin) and all specimens were found to be toxic. The highest toxicity of specimen was 7,650 mouse units (MU) in Y. nebulosus and 1,460 MU in S. japonica. However, the other specimens re-collected from that fish pier were also found to be highly toxic in Y. nebulosus, but nontoxic in S. japonica. Hence, Y. nebulosus was judged as the real causative fish in this food poisoning. The toxins were partially purified from the methanolic extracts of toxic fishes by ultrafiltration and Bio-Gel P-2 column chromatography. Cellulose acetate membrane electrophoresis and high performance liquid chromatography analyses demonstrated that tetrodotoxin was the causative agent of this food poisoning.