The planning of case report forms (CRFs) in clinical trials or databases in registers is mostly an informal process starting from scratch involving domain experts, biometricians, and documentation specialists. The Telematikplattform für Medizinische Forschungsnetze, an umbrella organization for medical research in Germany, aims at supporting and improving this process with a metadata repository, covering the variables and value lists used in databases of registers and trials. The use cases for the metadata repository range from a specification of case report forms to the harmonization of variable collections, variables, and value lists through a formal review. The warehouse used for the storage of the metadata should at least fulfill the definition of part 3 "Registry metamodel and basic attributes" of ISO/IEC 11179 Information technology - Metadata registries. An implementation of the metadata repository should offer an import and export of metadata in the Operational Data Model standard of the Clinical Data Interchange Standards Consortium. It will facilitate the creation of CRFs and data models, improve the quality of CRFs and data models, support the harmonization of variables and value lists, and support the mapping of metadata and data.