After an extensive review and assessment of the scientific evidence on the respiratory health effects of passive smoking, the U.S. Environmental Protection Agency has determined that the widespread exposure to environmental tobacco smoke in the United States presents a serious and substantial public health impact. The Environmental Protection Agency concluded that environmental tobacco smoke causes lung cancer in adult nonsmokers and increases the risk for a variety of noncancer respiratory disorders, especially in children. This article reviews evidence presented in the Environmental Protection Agency's 1992 report on the respiratory health effects of passive smoking and responds to critical allegations levied by Gio Gori in his article "Science, policy, and ethics: the case of environmental tobacco smoke", appearing in the same issue of this journal. Several recent studies appearing since the cutoff date for inclusion in the EPA report are also discussed.