HEI Communication 12 describes a project by Dr Scott Zeger and colleagues at the Johns Hopkins Bloomberg School of Public Health that was funded by HEI to make data and software from the National Morbidity, Mortality, and Air Pollution Study (NMMAPS) available to the wider research and policy communities. This Communication contains the Project Report, which describes the Internet-Based Health and Air Pollution Surveillance System (iHAPSS), along with Comments from some members of the HEI Health Research and Review Committees and other experts who had used the data.