All elective surgical procedures of the colon from 1992-1994 at Kreisspital Männedorf were analyzed retrospectively. The goal of this study was to find out if a preoperative autologous blood donation before elective colon surgery is useful and if so to determine the amount of blood to be donated. In 87 surgical procedures of the colon, the use of homologous blood transfusions was studied. The need for transfusion was highest in abdominoperineal resection with 6.8 (+/- 4.45) units and lowest in sigmoid resections with 0.68 (+/- 0.88) units. The estimated intraoperative blood loss was 868.67 (+/- 732.54) ml and 1.8 (+/- 2.6) units of homologous blood were transfused. The need for transfusion depended on the preoperative hemoglobin, the estimated intraoperative blood loss and the duration of the operation. We concluded that a preoperative donation of autologous blood before sigmoid resection is unnecessary. For all other colon resections with malignant or benign disease autologous blood transfusion is useful provided the patient meets the requirements for donation. A donation of 2 units of autologous blood is sufficient. With a preoperative hemoglobin value. > or = 11 g/dl and an estimated intraoperative blood loss < or = 1000 ml or an operation time < or = 150 min. the need for additional transfusion with homologous blood is minimal.