[en] The data for applying the reactor ''Yayoi'' for medical treatment was submitted to reactor controlling and operating committee of ''Yayoi'' institute on November 12, 1976 and explained. The preparations were made for the irradiation which was to be given to a patient with most desirable conditions on Dec. 24 by the reactor ''Yayoi''. The data on these preparations and preliminary tests were submitted. The patient died on December 11 without getting irradiation. For nuclear study, not only general and a long-term information but prompt action is also required to deal with the event within a limited time even if it is under the legal regulations. More data should be added to get more sufficient information for the future application. (Kobatake, H.)