Nonsmokers who live with smokers are at increased risk for chronic disease. This study evaluated the impact of eliminating smoking in the home on nonsmokers' environmental tobacco smoke (ETS) exposure. Nonsmokers participated in measurements of their ETS exposure before and after the smoker in their home quit smoking. A matched comparison group of nonsmokers from nonsmoking homes was also included. ETS exposure was assessed using passive nicotine monitors, an exposure diary, and a questionnaire. Nonsmokers from smoking homes had significantly higher exposure to ETS than those from nonsmoking homes. There was a 60% reduction in nicotine levels following smoking cessation by the household smoker. However, there were still detectable levels of nicotine measured at posttest. These results have important implications for individual risk reduction and public health policy.