Indoor air quality investigations conducted by the National Institute for Occupational Safety and Health (NIOSH) under the Health Hazard Evaluation (HHE) Program were briefly presented and reviewed. A total of 203 HHEs involving indoor air quality (IAQ) and completed through December 1983 were included in this review. Most of the evaluations have involved government and private offices (over 75 percent), educational institutions (14.8 percent), and health care facilities (9.3 percent). Classification of the findings of the IAQ evaluations showed that the source of the problem was inadequate ventilation in 48.3 percent of the cases, environmental contamination in 31.4 percent, humidity in 4.4 percent, hypersensitivity pneumonitis in 3.0 percent, cigarette smoking in 2.0 percent, noise/illumination in 1.0 percent, and unknown in 9.4 percent. A walk through evaluation with an industrial hygienist is the current approach to evaluating office environment requests. Environmental sampling, a medical study, a ventilation assessment or some combination of these may be required. Better methods for assessing indoor air quality are currently being developed by NIOSH.