The objective of this investigation was to determine the extent of areal and day-to-day variability of stationary environmental tobacco smoke (ETS) concentrations in a single large facility where smoking was both prevalent and unrestricted, and to determine the degree of daily variation in the personal exposure levels of ETS constituents in the same facility. The subject facility was a relatively new four-story office building with an approximate volume of 1.3 million ft3. The exchange of outside air in the building was determined to be between 0.6 and 0.7 air changes per hour. Eighty-seven area samples (excluding background) were collected at 29 locations over the course of 6 days of sampling. Locations included offices and cubicles occupied by smokers and nonsmokers, common areas, and the computer and mail rooms. Twenty-four nonsmoking subjects wore personal sampling systems to collect breathing zone air samples on each of 3 days in succession. This generated a total of seventy-two 8-h time-weighted average (TWA) personal exposure samples. In all samples, respirable suspended particulate matter, ultraviolet light-absorbing and fluorescing particulate matter, solanesol, nicotine, and 3-ethenyl pyridine were determined. With the exception of a few locations, tobacco-specific airborne constituents were determined in all samples. Not surprisingly, areas with the highest ETS constituent concentrations were offices and cubicles of smokers. Median and 95th percentile concentrations for all area samples, excluding background, were determined to be 1.5 and 8.7 microg/m3 for nicotine, and 8.2 and 59 microg/m3 for ETS-specific particles (as solanesol-related particulate matter, Sol-PM), respectively. Personal exposure concentrations of ETS components were similar to those levels found in the area samples (median nicotine and Sol-PM concentrations were 1.24 and 7.1 microg/m3, respectively), but the range of concentrations was somewhat smaller. For example, the 95th percentile 8-h TWA nicotine and ETS-specific particle (as Sol-PM) concentrations were 3.58 and 21.9 microg/m3, respectively. Intrasubject variation of daily concentrations ranged from 20% to 60%, depending on the component. Self-reported proximity to smokers was supported by higher ETS concentrations determined from the personal monitors, but only to a modest extent. Although smoking was completely unrestricted inside the main office areas of the facility, ETS levels, either areal or from personal exposure measurements, were lower than those estimated by Occupational Safety and Health Administration to be present in such facilities.