Retrospective conversion as a conversion of data from an old to a newer format is usually realized as a transfer of card catalogue into a computer form in a fast and simple way. The National and University Library in Ljubljana, Slovenia, started its first retroconversion project in 1997 with the oldest, partly handwritten catalogue, covering the period 1774-1947. The description of the catalogue is given, taking into account both cards' characteristics (size, handwritten/typewritten, scripts used etc.) and different cataloguing rules applied at that period (Austrian Library Instruction, Prussian Instructions etc.). The whole process was divided into separate phases according to technologies and human resources available, and specific procedures weredesigned (trancription, manual and automatic structuring, control etc.). The result are ca. 70,000 records in MARC format, which were included into existing library catalogue. Records for items published until 1830 were contributed to Consortium of European Research Libraries (CERL) Hand Press Books database hosted by Research Libraries Group (RLG). NUL is currently working on retroconversion of remaining catalogues (ca. 300,000 records) where different procedures have to be designed due to different characteristics. The experiences gained during these projects may be found useful by other libraries that are either starting or considering retrospective conversion.