Public concern has been heightened in recent years regarding headaches, lethargy, eye, nose and throat irritation, breathing difficulties, and dry skin reported among inhabitants of large, mechanically ventilated buildings. The role played by the ventilation systems in such buildings is not clear. One important aspect of building ventilation is the rate at which outdoor air is introduced to the building per person. Guidelines have been incorporated into building codes and to the regulations as standards, setting the minimum outdoor air ventilation rate that the ventilation system must have in a new building. The editors suggest that since it is impractical to collect toxicity information on all indoor pollutants of concern, empirical data on worker symptoms at different outdoor air ventilation rates may prove useful. Studies are needed in a greater variety of buildings, over longer periods of time, and with improved measurements of the outdoor air ventilation rate, various indoor exposures, and health outcomes. Existing scientific findings suggest that standards for outdoor air ventilation rates in occupied buildings may be reasonable, particularly if they are bolstered by further study.