An environmental investigation is performed when difficulty is encountered in identifying the probable source of a contamination. These inspections are usually done by an industrial hygienist or a building inspector with special microbial training. During the evaluation of the patients presented in these papers, the investigation was done by Dr. Jacobs. Each investigator may utilized somewhat different techniques and devices to augment the visual inspection. The exterior is investigated for evidence of broken concrete slabs, moist areas of the surface around the home, deterioration of walls, and damage to the roof. Sites are entered and checked for odors followed by a walk through the entire home looking for evidence of water damage, excessive dusts on surfaces, and any obvious mold growth. A gravity culture technique under controlled conditions, an Andersen Sampler, or other similar devices may be utilized to confirm the presence of a microbial contamination. Another device that may be utilized to aid in locating a source of moisture and, therefore, the most likely site of contamination is a moisture meter. These devices are used by house painters to determine if surfaces are dry enough to paint and can detect differences in moisture content from one wall or floor area to another.