Environmental sampling to determine the presence of Bacillus anthracis spores in indoor environments is an important tool for assessing risk for exposure. Sampling can also be used to determine the extent and degree of contamination, to support decisions regarding the need for medical treatment or cleanup, and to provide guidance regarding when cleanup is adequate to permit re-entry into an area. The decision to collect samples should be made by industrial hygienists and other experts familiar with organism and the sampling methodologies. Representatives from laboratories, as well as local, State, and Federal agencies, should be consulted during the decision-making process. The decision should be based on the extent and location of any suspected contamination, the potential for the contaminant to migrate, and the activity for which the facility is used. No occupational or environmental exposure standards currently exist for B. anthracis spores. There are no validated sampling and analytical methods specifically for B. anthracis in environmental samples. Data are lacking on collection efficiency of the sample collection media for typical porous and nonporous surfaces encountered in indoor environments. The effect of varying concentrations of B. anthracis-containing particles and dust loading on sampling efficiency has not been studied. The recovery efficiency of the analytical methods has not been adequately evaluated and limits of detection have not been established. The confirmatory test for environmental samples is culture with positive identification of B. anthracis (CDC culture method). These methods are believed to be more sensitive than the available hand-held rapid-assay devices for the detection of B. anthracis. Immune-based assays should not be used alone for B. anthracis but should be confirmed with samples analyzed by culture methods to make public health decisions. This is based on the experience of CDC field investigators and laboratory technicians during the recent anthrax response investigations and experience with environmental monitoring for other contaminants in indoor environments. Further research is needed to clarify the sensitivity of the sampling and analytical methods for known or suspected B. anthracis.