Approximately one hundred nonsmoking individuals in each of 16 metropolitan areas of the United States collected a sample of air from their breathing zone while in their workplace and a sample while away from work during their 24-hour days. Individuals were selected for the study in an attempt to equally represent those working and living in smoking and nonsmoking environments. Collected samples were analyzed for respirable particulate matter (RSP) (3.5 microns diameter), ultraviolet absorbing particulate matter, fluorescing particulate matter, solanesol, scopoletin, nicotine, 3-ethenyl pyridine, and myosmine. Individuals living and/or working in environments where smoking occurs were confirmed to be the most highly exposed to environmental tobacco smoke (ETS). Residential RSP levels ranged from 50 to 113% of those which have been reported by other investigators. For the majority of subjects who either lived or worked in smoking environments, the home was found to be the greater source of ETS exposure. Exposures of subjects whose spouses smoked unrestrictedly within the home were a factor of two to four higher than those of subjects who worked in locations where smoking occurred and was not restricted. Exposures of typical subjects to nicotine in the workplace were 30-60% of those estimated by the Occupational Safety and Health Administration (OSHA) and 15-20% of those estimated by the OSHA for the most highly exposed workers.