In May, 1961, the paralytic food poisoning broke out by Akazara shellfish (Chlamys Nipponensis Akazara Kuroda) in Ofunato city, facing the Pacific Ocean, Iwate Prefecture, the north eastern part of Japan. For the purpose of preventing the poisoning, in the following year, 1962, from February to December, Akazara shellfishes were collected periodically from the bay and the relationship between the temperature of the sea water and the variation of its toxicity was investigated. The results were as follows:(1) In 1962, the toxic phenomenon was observed in the same period of the year as that of 1961, but there were some differences in its toxicity. The trend of the toxicity decrease was almost similar in both cases.(2) The toxicity became maximum from the beginning to the middle of June, but it was one week earlier than at Shizu situated at the mouth of the bay that the toxicity of shellfish caught at Yamaguchi located at the end of the bay reached the highest.(3) The temperatures of sea water at the bay Ofunato, Kamaishi adjacent to Ofunato, and Miyako, all of which face the Pacific, was not found to be considerably different. Furtheremore there were no significant difference among the sea water temperatures of Ofunato bay from 1960 to 1962.(4) In 1962, the relationship between the poisonous period and the temperature of sea water (at Yamaguchi and Shizu) was co-relative. The temperature of sea water showing the maximum toxicity was 9.6-13.8°C and it was almost same as reported by Sommer et al.