The operating theater blood transaction system (OTBTS) is a virtual blood banking system that allows computer crossmatch-compatible blood ordering and delivery in the operating theater remote from the hospital blood bank. It was developed and implemented in our hospital in 1997 and was expanded in 2002 to include an unmatched blood module that allows ordering and issuing unmatched RBCs for intraoperative transfusion. During the past 7 years, the system has handled 6,333 crossmatch requests for intraoperative transfusion and issued 20,073 units of RBCs, including 100 units of unmatched RBCs (group O, 72 units; group-identical, 28 units). The OTBTS has proven to be efficient (with a turnaround time for blood ordering and issuing < 30 seconds), effective (with a reduced crossmatch/transfusion ratio and blood wastage), and error free (no delay or error in transfusion or postponement of operation). Furthermore, our experience with the unmatched blood module has attested to the safety and efficacy of computer-controlled, online ordering and real-time, on-site delivery of unmatched RBCs for emergency transfusion.