Between October 30 and November 4, 2000, eleven persons were intoxicated due to ingestion of a serranid fish Epinephelus sp. in Kochi Prefecture, Japan. Their symptoms were mainly featured by severe muscle pain, low back pain, and discharge of black urine. Serum creatine phosphokinase (CPK) levels of victims were higher (700-23,800 IU/l) than normal values, and their recovery times were more than one month. Immediately after the incident, the leftovers were collected for investigation. The causative agent was identified as palytoxin (PTX) on the basis of delayed haemolytic activity which was inhibited by an anti-PTX antibody and ouabain (g-strophanthin). To our knowledge, this is the first report on palytoxin poisoning with serranid fish.