This represents the first in a series of lectures sponsored by the Agency to present a range of perspectives on controversial environmental and health issues from the vantage points of distinguished scientists. The views expressed are, therefore, not necessarily the views of the U.S. EPA. The lecture discusses what is known about the health and carcinogenic effects associated with low doses of ionizing radiation. It points out the scientific consensus that there are no reproducible studies unequivocally demonstrating the effects of low-level ionizing radiation and distinguishes between scientific fact and public policy.