The separation of a colony of the Spontaneously Hypertensive Rats (OKAMOTO and AOKI) (SHR) was reported in 1962 and 1963. At that time the following points regarding these rats were described: (I) The incidence of hypertension was 100 per cent in the rats over several months of age. (2) The blood pressure was markedly high. (3) These rats showed hypertensive cardiovascular diseases in high frequency at the advanced stage of hypertension. Therefore, it was emphasized that SHR was by far an excellent material for hypertension research in contrast with the other animals with spontaneous hypertension or with already known experimental hypertensions. Since then 10 years have passed. Meanwhile, we established an inbred strain of SHR at the Department of Pathology, Faculty of Medicine, Kyoto University, in October, 1969. Various and numerous reports, more than 150 were published on SHR not only from our Department but also from some of more than 100 domestic and foreign laboratories and institutions to which these animals were donated. Finally, time was ripe for an inter­ national symposium on this SHR, which was held on Oct. 18-22, 1971 in Kyoto as U.S.­ Japan Seminar on Spontaneously Hypertensive Rats (organizers; U.S.-S. UDENFRIEND, Ph. D., Japan-K. OKAMOTO, M. D.). In this seminar 25 members and 22 observers from the U.S., Japan and other countries participated. They presented 46 reports in 9 sessions, joined the lively discussions and obtained satisfactory results.