Food poisoning caused by histamine occurs in 7 to 20 cases every year, and the main cause is the intake of improperly managed red-fleshed fish such as tuna. Histamine is produced from free histidine in fish meat. The changes of the amount of histamine and the amount of free histidine when stored at 5 ℃, 10 ℃ and 25 ℃ was examined for commercially available seafood. A maximum of 724 mg/100 g of histamine was detected in red-fleshed fish, and a maximum of 11.2 mg/100 g was detected in other seafood. A decrease in the amount of free histidine was confirmed in seafood in which histamine was detected. The amount of histamine produced from free histidine was about the same.