Introduction With the aid of the exchange transfusion nomogram of Figure 1, the physician can rapidly plan and analyze an exchange transfusion. By applying a straight edge to the nomogram, any of three essential parameters of the exchange can be determined quickly if the other two are known. The parameters are: ( a ) donor blood volume, ( b ) recipient blood volume, and ( c ) per cent exchange accomplished. The nomogram is based on the exchange transfusion formula proposed in Reference 1 and readily allows inclusion of tubing dead space effects described in Reference 2. There follows a review of the terms used in discussing exchange transfusions, succeeded by several examples illustrating the use of the nomogram. Mathematical considerations which delimit the validity of the nomogram are presented in an appendix. An exchange transfusion takes place when a quantity of patient blood is withdrawn and replaced by an equal quantity of donor blood. If