Three hundred and three patients undergoing elective surgery were studied prospectively. Patient data and results of serial blood cell counts were recorded before and after surgery and used to evaluate the criteria used to reserve and transfuse blood and blood products, as well as to assess the outcome of transfusions performed. Six hundred and ninety-nine units were reserved, indicating a reservation-to-transfusion ratio of 1.8. The most often cited reasons for reserving blood were surgical technique, nature of disease and prolonged surgery. A high number of reservations were called for from the ward by the surgeons themselves. A total of 180 patients were given transfusions, the main reason being the anesthesiologist's judgement that the Hb count was low (in 26% of cases). Transfusions because of slight bleeding during surgery and prolonged surgery gave rise to the highest Hb counts. The lowest post-transfusion Hb counts recorded occurred when the reason cited was presence of signs of anemia. We conclude that the ratio of reservations to transfusions in our study was acceptable, as were the reasons justifying reserves. There is an overall tendency to achieve excessively high Hb counts (10-11 g/dl) in the early postoperative period. The best criterion for performing transfusion is the presence of signs of anemia.