Historical data in the public health record represent natural experiments in human disease ecology, and have long been used to develop and test ecological theory on host-pathogen interactions. Dr Wearing will present analysis of a new dataset of measles epidemics in the United States from 1925 to 1945, consisting of weekly case reports in 74 cities and 45 states. The dataset is remarkable for its wide geographic extent as well as for the significant demographic changes that occurred during the time period.