WHILE recently there has been much emphasis placed on the examination of the effects of chronic irradiation on intact whole forest ecosystems, the response of individual forest species following acute irradiation has received much less attention. At present only a limited amount of information is available concerning the effects of acute irradiation on the genus Pinus. Working at Brookhaven, Sparrow et al. have reported on Pinus strobus1, and a second group under Shields has reported on Pinus monophylla2. The purpose of the work recorded here was to examine the response of Pinus thunbergii seedlings to acute γ-radiation under controlled laboratory conditions as opposed to that under the field conditions as examined by other workers1,2.