American Academy of Environmental Medicine in 1984. This organization offers a definition of multiple chemical sensitivity which is also referred to as ecologic illness: "Ecologic illness is a poly-symptomatic, multi-system chronic disorder manifested by adverse reactions to environmental excitants, as they are modified by individual susceptibility in terms of specific adaptations. The excitants are present in air, water, drugs, and our habitats." Clinical ecology has been controversial, and committees of other specialty organizations have considered its diagnostic and therapeutic approaches to be inadequately supported by published studies (American Academy of Allergy and Immunology 1986; California Medical Association 1986; American College of Physicians 1989). Several recent reviews provide a more comprehensive background on multiple chemical sensitivity (Cullen 1987, Bascom 1989, Ashford and Miller 1991).

Although the literature addressing multiple chemical sensitivity is increasing, information on its frequency and natural history is lacking. Even defining multiple chemical sensitivity and developing criteria for diagnosis have proved difficult. Diverse pathogenic mechanisms have been postulated, but experimental models for testing them have not been established.

At the request of the Environmental Protection Agency, the National Research Council conducted a workshop to develop a research agenda to study the phenomenon of multiple chemical sensitivity. The workshop was convened with the overall objective of addressing the gaps in the scientific evidence on multiple chemical sensitivity. Workshop participants were multidisciplinary and included clinicians, immunologists, toxicologists, epidemiologists. psychiatrists, psychologists, and other involved in research or clinical activity relevant to the problem. The participants had an extensive range of experience and views on multiple chemical sensitivity. Three groups were formed to develop a research agenda. The subjects assigned were 1) case evaluation and criteria for diagnosis 2) mechanisms potentially underlying multiple chemical sensitivity and 3) epidemiologic approaches to investigating multiple chemical sensitivity.

This volume includes the papers prepared and presented by individual workshop participants; the papers have not undergone peer review. The papers offer a variety of views of the pathogenesis of multiple chemical sensitivity, its definition and diagnosis, and its management. They also illustrate the range of opinions as to the legitimacy of multiple chemical sensitivity as a unique clinical entity and the approaches used to treat it.

The paper by Lebowitz reviews key concepts of sensitization central to considering possible immunologic mechanisms of multiple chemical sensitivity. Lebowitz points to the distinction between sensitization (sensitized persons respond at lower doses than nonsensitized persons) and irritation. Burrell and Meggs also address the immune system and multiple chemical sensitivity; multiple chemical sensitivity is not seen as consistent with the specificity of immune responses, and authors point to immune mechanisms that might produce this phenomenon.

Bell emphasizes the need to use an integrated neuropsychiatric and biopsychosocial approach in considering multiple chemical sensitivity. Both she and Miller and Ashford suggest a possible role of the limbic system in triggering by odor. Experimental approaches to addressing mechanisms are described by Karol (an animal model) and by Meggs ( a clinical research protocol).

Miller and Ashford address the difficult problem of defining multiple chemical sensitivity, offering this operational definition: "The patient with multiple chemical sensitivity can be discovered by removal from the suspected offending agents and by rechallenge, after an appropriate interval, under strictly controlled environmental conditions.

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