Over the past several years, scientists, public health officials, and policy makers have become increasingly interested in understanding how the emergence and spread of infectious diseases could be affected by environmental factors, particularly variations in climate. In September 1995 the Institute of Medicine/ National Academy of Sciences and the National Science and Technology Council held a Conference on Human Health and Global Climate Change. Following this event, an interagency discussion group met several times and decided that a more in-depth exploration of this issue was needed, and thus plans were developed for this study on climate, ecosystems, infectious diseases, and health (CEIDH)