The object of this essay has been to investigate the interlibrary loan service at the university libraries of Borås and Kalmar. For this purpose a quantitative and a qualitative method have been used. The main body of information consists of statistic data concerning the incoming interlending orders for a three-month-period. In order to examine the circumstances under which the interlending activity exists several interviews were made. The study showed that there are several important factors which together make up the complexity that governs the interlending activity. What type of demand there is depends on the educational level, whether the different study programmes have a broad or limited subject orientation or not, and if the demand is of a constant or an inconstant nature. Well-established routines at the information-desk and co-operation with the departments of the different study programmes are important factors in keeping the knowledge of what books and serials are needed up to date.