Summary A number of major European culture collections, supported by the “Biotechnology Action Programme” (BAP) of the European Community (EC) are involved in the establishment of the multinational “Microbial Information Network Europe” (MINE). It has been realized that the adoption of a uniform format for computer storage and retrieval of strain data is essential, considering that it is the scope of the project to allow the electronic combination of data from different collections, and thus facilitate the publication of integrated catalogues or searching different databases using common commands. The format for bacteria is different to that previously published for fungi and yeasts (Gams et al., 1988) in several important respects, largely relating to the differences in cytological properties and taxonomic treatment. In addition to the main data set, “species records”, two other data sets, “strain records” and “synonym records” may be linked together. A minimum data set of 24 fields (similar to the fields used in catalogue production) is defined which facilitates the exchange of data between the national nodes and serves as a directory to strains available at other nodes. A total of 133 fields are proposed that can be grouped in the following ten blocks: internal administration - name - strain administration -environment and history - properties (cytological, biomolecular data) - mutants, plasmids, and phages - growth conditions - chemistry and enzymes - biological interactions - practical applications. Several fields are to be divided into subfields at different ranks. Delimiters are used to either separate a range of entries that are to be indexed or to divide an entry from the reference to its source or remarks that are not to be indexed. In this paper the contents and structure of the fields proposed for bacteria are characterized and often illustrated by examples. Uniformity of input is essential for indexed fields and desirable for non-indexed fields. Five thesaurus files are envisaged to ensure consistency.