This is the ninth substantive report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)a to the General Assembly.b As anticipated in its 1982 report. UNSCEAR had been planning to conduct detailed studies on selected subjects, together with comprehensive assessments of the type normally issued. This report contains reviews of three special topics in the field of biological effects of ionizing radiation that are among those presently under consideration by the Committee: genetic effects of radiation (annex A). dose-response relationships for radiation-induced cancer (annex B), and biological effects of pre-natal irradiation (annex C).