The Health Insurance Study (HIS) is a complex multiyear longitudinal study of the role of health insurance in the utilization of health care services. As part of this study, a large database is being constructed using information gathered by numerous data collection documents. Because of the nature and size of the database, it is important that a systematized archive be maintained which presents an overview of the data contained in the data files. Central to this archive is the Data Element Dictionary providing a formal reference point for the proper usage, meaning, and manipulation of the data elements. This paper discusses the role of the dictionary in the HIS information system. 14 pp. Bibliog.