We introduce the design of replacement donor programs and blood allocation schemes as a new application of market design. We propose novel blood allocation mechanisms that accommodate fairness, efficiency, and various other allocation objectives, together with the possibility of endogenizing exchange rates between received and donated blood units beyond the classical one-for-one exchange. These mechanisms also provide correct incentives for the patients to bring forward as many replacement donors as possible. This framework and the class of mechanisms are applicable to general settings of multi-unit exchange of indivisible goods with compatibility-based preferences beyond blood allocation.