Arai" (washing) is a traditional cooking method of fish preparation in Japan. Carp muscle slices were washed in water (49°C for 15 set, or 0°C for 10 min), and examined for physical and biochemical changes. At 49"C, rigor-mortis was accelerated, resulting in a marked decrease of muscle slice thickness. ATP degradation proceeded faster at 49°C than at 0°C. Arai treatment at 49°C increased myofibrillar M$+ -ATPase activity 8-9 times in the absence of Ca2+, but did not affect activity in the presence of Ca*+ as much, giving only a 1.2 times increase.