Surveys have provided magnificent information about the health of the American people, but they rarely contribute to our understanding of how medical services affect people's health. The authors explore the opportunity to harness the medical services system to provide information that clarifies the relationship between people's health and the services they receive. They also note the risk posed by managed care-that competition and cost-cutting may pit the health industry against access to and standardization of health services data--but see hope in recent legislation.