Ventilation rates have been measured in 38 commercial buildings representing a variety of use types, sizes, ages, and mechanical system configurations. A single tracer (SFe) test was conducted once in 36 buildings over a two- to four-hour period based on mechanical system operation for a prior two-week period= Two buildings were tested twice under different environmental conditions. Whole-building ventilation rates ranged from 0.3 air changes per hour (ach) to 4. 2 ach for the 40 building measurements, with an average value of 1.5 ach. Minimum ventilation rates were estimated in 13 of the 38 buildings. These values reveal that four of the 13 buildings have minimum ventilation rates that are less than the ASHRAE ventilation standard of 10 L/s occupant for smoking occupancies. Several pollutants were monitored in the buildings for lO-day periods during working hours. The pollutant group that most frequently approached or exceeded recognized guidelines was respirable suspended particles; the elevated concentrations were usually associated with nearby tobacco smoking.