There is a growing interest in biological markers of exposure to chemicals and in markers of adverse health effects from such exposures. Reflecting this interest, a new journal, Biological Monitoring, is being published by The Telford Press. The National Academy of ScienceslNational Research Council’s Board of Environmental Studies and Toxicology, at the request of the Environmental Protection Agency and the National Institute of Environmental Health Sciences, has established a Committee on Biological Markers to evaluate the scientific basis, current state of development, validation, and use of biological markers in environmental health research. * What are biological markers, or biomarkers, as they are sometimes called? The term “biomarker” refers to the use made of a piece of information, rather than to a specific type of information. A biomarker is a change in a biological system that can be related to an exposure to, or effects from, a specific xenobiotic or type of toxic material. An ideal biomarker of an exposure is one that is chemical specific, detectable in trace quantities, available by noninvasive techniques, inexpensive to assay, and quantitatively relatable to a prior exposure regimen. An ideal marker of an effect or of a disease state is unique to the disease state in question and quantitatively relatable to the degree or stage of the disease. Few if any biomarkers will have all the above characteristics, but many nonideal biomarkers can be useful for specific purposes.