Alcohol use is highly prevalent among U.S. college students, and alcohol-related problems are often considered the most serious public health threat on American college campuses. Although empirical examinations of college drinking have relied primarily on self-report measures, several investigators have implemented field studies to obtain objective measures of alcohol consumption (blood alcohol concentration) from students in ecologically valid settings. This article describes the methodology of breath-test field survey that is being conducted on the grounds of San Diego State University. Descriptive summaries of the data collected through spring 2003 are provided, and limitations to methodology are discussed.