We developed a web-based program for a national surveillance system to determine baseline data regarding the supply and demand of blood products at sentinel hospitals in South Korea. Sentinel hospitals were invited to participate in a 1-month pilot-test. The data for receipts and exports of blood from each hospital information system were converted into comma-separated value files according to a specific conversion rule. The daily data from the sites could be transferred to the web-based program server using a semi-automated submission procedure: pressing a key allowed the program to automatically compute the blood inventory level as well as other indices including the minimal inventory ratio (MIR), ideal inventory ratio (IIR), supply index (SI) and utilisation index (UI). The national surveillance system was referred to as the Korean Blood Inventory Monitoring System (KBIMS) and the web-based program for KBIMS was referred to as the Blood Inventory Monitoring System (BMS). A total of 30 256 red blood cell (RBC) units were submitted as receipt data, however, only 83% of the receipt data were submitted to the BMS server as export data (25 093 RBC units). Median values were 2.67 for MIR, 1.08 for IIR, 1.00 for SI, 0.88 for UI and 5.33 for the ideal inventory day. The BMS program was easy to use and is expected to provide a useful tool for monitoring hospital inventory levels. This information will provide baseline data regarding the supply and demand of blood products in South Korea.