The geographic distribution of Lyme disease in the U.S. is currently known only from human case report data obtained by the CDC’s national surveillance system for Lyme disease. The usefulness of these surveillance data is limited by the application among states of different surveillance methods, lack of detection, under-reporting, and misclassification of cases. There exists a great need to improve this information base to better define the distribution and ecological determinants of Lyme disease risk throughout the U.S. We propose to develop methods to identify ecological parameters predictive of entomologic risk for Lyme disease. We plan to test the predictive accuracy of these methods for distinguishing endemic and non-endemic areas, and for measuring human risk where Lyme disease is endemic. We also propose to apply these methods to develop a national Lyme disease risk map in cooperation with CDC that will include ecological data delineating the geographic distribution of risk.