Adequate information is available linking ETS to several medical problems, including respiratory illnesses in children and lung cancer in adults; nonetheless, continuing investigation is necessary to clarify several issues. Reliable information needs to be gathered on the quantity and fate of ETS chemicals in ordinary indoor environments; improved surveys quantifying passive smoke exposure should be tested along with the use of biologic markers to quantify exposure-dose relationships in nonsmokers. To date, legislation and private initiatives have been the most promising of the various measures to protect nonsmokers from ETS. While nonsmokers' judicial action has had variable success, it places the burden of challenging smoking on the nonsmoker, and it entails piecemeal, case-by-case resolution. On the other hand, legislation and private policies relieve the nonsmokers' burden to initiate the challenge, and they protect greater numbers of nonsmokers. Furthermore, legislation and policies may have a great number of direct and indirect effects. In the short term, legislation and policies that are adequately implemented and enforced alter the behavior of smokers in areas where smoking is prohibited and should result in a reduced concentration of tobacco smoke in those areas. In the long term, policies and legislation that restrict smoking in public places and the workplace help to reinforce nonsmoking as the normative behavior in society. Smoking restrictions increase public awareness and acceptance of health risks of tobacco smoke. The combination of altered social norms and reduced opportunities to smoke may encourage smokers to quit and nonsmokers, especially adolescents, not to start.