Since 2000, U.S. government health research agencies have spent almost $1 billion on an effort to churn out thousands of 3D structures of proteins. The Protein Structure Initiative (PSI) funded large teams of biologists, physicists, chemists, and engineers to transform the science of protein analysis. So far, PSI investigators have worked out the structures of 6507 proteins. But last fall, a National Institute of General Medical Sciences advisory council bowed to long-standing criticism of the program and pulled the plug, allowing its current round of funding to expire in June 2015. Now, researchers and policymakers are asking what the huge experiment learned and what its demise will mean for the future of structural biology in the United States.