The AIDS epidemic has focused considerable attention on the risks associated with blood transfusions. Perhaps of more importance, hemolytic transfusion reactions and post-transfusion non-A non-B hepatitis continue to be significant concerns. However, guidelines for blood transfusions in the surgical patient vary considerably in the medical literature. Some recent texts stress the need to consider factors such as patient's age, surgical procedure, co-morbid illness, predicted blood loss, and cause of the anemia, as well as the hemoglobin level. Nonetheless, in practice many surgeons still adhere to the 10g/dl threshold for transfusion. The lack of consensus guidelines can probably be attributed to the dearth of studies exploring the indications for transfusion. The few studies which have examined this question are limited because they fail to analyze subsets of patients by age, co-morbid illness, or blood loss. The need to develop peri-operative transfusion guidelines based on multivariate analysis, therefore decreasing the frequency of unnecessary transfusions resulting from the common use of a hemoglobin threshold, is especially important in light of the hazards and costs associated with blood transfusions. Jehovah's Witnesses were chosen as the study population because they decline blood transfusion for religious reasons.