Guarantor: N Slimani. Contributors: NS was the overall coordinator of the ENDB project and in charge of the preparation of the paper in collaboration with the other co-authors. GD, JV, GS, SS, MP, IU, DATS, NS were members of the 'task force group' involving specific managerial or technical tasks for the project and/or the preparation of reference ENDB guidelines. IU was also in charge of the development of the DBMS in collaboration with the coordinating centre. SS, MP, PG, AM, JI, WB, AF, SW, EV, JU, SC and AB were involved as the national compilers in charge of documenting, compiling and evaluating the subset of their national nutrient databases used in the ENDB project. AM, JI, WB and IU were also involved as members of the 'ENDB expert group' headed by DATS, in charge of revising the reference ENDB guidelines. MN, MCB-R, CS, AT, SN, IM, JR, HB, MO, PHMP, PJ, PA, DE, EL, MS de M, AT, KG, CS, SR, AW, SB were involved as local EPIC collaborators in the supervision and preparation of EPIC-specific databases relevant to the ENDB project (e.g. recipe files). CC and MvB, at the coordinating centre, were involved in tasks relevant to these EPIC databases. AFS has provided long-standing scientific collaboration and support for setting up the ENDB. ER is the overall coordinator of the EPIC study. All co-authors provided comments and suggestions on the manuscript. Objective: This paper describes the ad hoc methodological concepts and procedures developed to improve the comparability of Nutrient databases (NDBs) across the 10 European countries participating in the European Prospective Investigation into Cancer and Nutrition (EPIC). This was required because there is currently no European reference NDB available. Design: A large network involving national compilers, nutritionists and experts on food chemistry and computer science was set up for the 'EPIC Nutrient DataBase' (ENDB) project. A total of 550-1500 foods derived from about 37 000 standardized EPIC 24-h dietary recalls (24-HDRS) were matched as closely as possible to foods available in the 10 national NDBs. The resulting national data sets (NDS) were then successively documented, standardized and evaluated according to common guidelines and using a DataBase Management System specifically designed for this project. The nutrient values of foods unavailable or not readily available in NDSs were approximated by recipe calculation, weighted averaging or adjustment for weight changes and vitamin/mineral losses, using common algorithms. Results: The final ENDB contains about 550-1500 foods depending on the country and 26 common components. Each component value was documented and standardized for unit, mode of expression, definition and chemical method of analysis, as far as possible. Furthermore, the overall completeness of NDSs was improved (X99%), particularly for b-carotene and vitamin E. Conclusion: The ENDB constitutes a first real attempt to improve the comparability of NDBs across European countries. This methodological work will provide a useful tool for nutri...