The international system of ISSN followed the changes that have been going on in document typology, typography and reprography. According to the standard and manual of ISSN the 60 national centres have to prepare the bibliographic description of domestic serials, disregarding their media, and the descriptions must be forwarded to the international database in USMARC format, the exchange format of the system modified by new fields and codes. Modifications did not cause any problems to.the centres using the ISSN-OSIRIS database management system. Descriptions follow the principles of ISBD/S, and those of electronic documents are revised on the annual sessions of the representatives of national centres. These centres make efforts to give the most complete possible description of their periodicals for the international database of ISSN. The Hungarian ISSN centre registers publications on floppy disc or CD-ROM as they are submitted to the legal deposit service, however, they are able to include online publications in their registries only since proper network connections have been established.