Diagnosing problem buildings is in many cases a challenging and complex task. As a result of increasing needs, a number of public and private groups have developed standardized protocols for conducting problem-building investigations. A detailed investigative protocol designed to meet the needs of industrial hygienists who conduct problem building investigations has been recently developed by the American Industrial Hygiene Association (AIHA). Though including elements of other protocols, it for the most part reflects the experiences of industrial hygienists who have conducted problem-building investigations. Many of the early problem-building investigations were conducted by industrial hygienists who employed traditional industrial hygiene concepts and methodologies. Investigative protocols developed by the National Institute of Occupational Safety and Health (NIOSH) and the AIHA represent major efforts by industrial hygienists to develop systematic investigative procedures which are less constrained than traditional practices. In the United States, problem-building investigations are very commonly conducted by private consultants associated with firms that provide specialized IAQ or IH services.