We describe a set of programs for creating and using indexes for the distributed forms of the major sequence libraries. The indexes conform to the specification of those distributed on cd-rom by the EMBL sequence library. The programs create entry name, accession number, author and freetext indexes and a brief directory index. If a suitable application program is given an entry name or accession number these indexes allow rapid retrieval of sequences or annotation. Similarly the author and freetext indexes provide the data for extremely fast searching on author names and "keywords". The indexing programs can create indexes for EMBL, Swiss-Prot, GenBANK, PIR and NRL3d libraries. We also describe the organisation and use of the different sequence libraries and their index files.