The institution of ?electronic markets as services? needs careful design. In this context, Market Engineering provides a structured design process that guides the market designer in this demanding task. In analogy to the engineering design process, the design stage of the Market Engineering process is decomposed into four major phases being the conceptual design, embodiment design, detail design and implementation. While the conceptual design phase is concerned with the formulization of the problem and the search for abstract solutions, the embodiment design refines the abstract concepts to blueprints that serve as a representation format for further design steps. So far, there was no applicable service blueprinting approach for market engineering. The paper illustrates that protocol diagrams from Agent UML (an UML extension) can serve as the basis for powerful modeling technique for blueprints of electronic market services.