The preparation of the present report of the United Nations Scientific Committee on the Effects of Atomic Radiation 1 took place at the twenty-third to the twenty-sixth sessions of the Committee. Professor L. R. Caldas (Brazil), Professor F. H. Sobels (Belgium) and Dr. C. B. Guzman Acevedo (Peru) served as Chairman, Vice-Chairman and Rapporteur, respectively, at the twenty-third session. Professor F. H. Sobels (Belgium), Dr. M. Klimek (Czechoslovakia) and Professor Z. Jaworowski {Poland) served as Chairman, ViceChairman and Rapporteur, respectively, at the twentyfourth and twenty-fifth sessions; and Dr. M. Klimek (Czechoslovakia), Professor F. E. Stieve {Federal Republic of Germany) and Dr. K. Sundaram {India) served in the same capacity. respectively, at the twenty-sixth session