Blood transfusion during cardiac surgical procedures has steadily decreased, but little information is available regarding the factors that determine its necessity or amount. To determine the predictors of blood utilization during myocardial revascularization, 441 consecutive patients undergoing primary myocardial revascularization were studied. Forty-four patients (10%) received blood during hospitalization with a mean transfusion of 0.3 +/- 1.4 units per patient. Age, sex, weight, body surface area, preoperative hematocrit, blood volume, and red blood cell volume were examined univariately for trends. All demonstrated a statistically significant trend for both need and amount of transfusion (p less than 0.001). Neither number of grafts nor duration of cardiopulmonary bypass demonstrated statistically significant trends. All univariately significant factors were evaluated by multivariate logistic regression analysis. Red cell volume was the best predictor of the need for transfusion (p less than 0.001), followed by age. No other factors improved predictive capabilities. We conclude that preoperative red cell mass and age are the principal determinants of the need for and quantity of blood transfused during myocardial revascularization. Use of this information may greatly improve the efficiency of ordering blood before operation.