Public concern and awareness are growing about adverse health effects of exposure to environmental contaminants. Frequently patients present to their physicians with questions or concerns about exposures to such substances as lead, air pollutants and pesticides. Most primary care physicians lack training in and knowledge of the clinical recognition, management and avoidance of such exposures. We have found that it can be helpful to use the CH2OPD2 mnemonic (Community, Home, Hobbies, Occupation, Personal habits, Diet and Drugs) as a tool to identify a patient's history of exposures to potentially toxic environmental contaminants. In this article we discuss why it is important to take a patient's environmental exposure history, when and how to take the history, and how to interpret the findings. Possible routes of exposure and common sources of potentially toxic biological, physical and chemical substances are identified. A case of sick-building syndrome is used to illustrate the use of the mnemonic.