We report a collective tuna fish poisoning which developed on June 10, 1988, in a staff dining room in Castellón. Twenty-one people were involved (attack rate 42.9%). The major symptoms were diarrhea, abdominal pain, headache, facial flushing and oral burning. The mean duration of the symptoms was 15 hours. The ingestion of tuna fish was significantly associated with the illness (p less than 0.001) when the other foodstuffs were controlled. Tuna fish had been defrosted at room air temperature during 14 hours. The analysis of several foodstuffs (there were no tuna fish remains available) and the food handling staff did not disclose pathogens. We discuss the etiology, pathogenesis, epidemiology and control of this type of food poisoning.