This article seeks to explain why blood banks and plasma companies reacted di¡erently to the same information about the spread of a new disease through the blood supply in the United States. I draw on recent work in economic sociology and the sociology of risk in order to give an account of these events. Using the concept of a “negotiated information order” to frame the analysis, I explain why blood banks and plasma companies acted as they did. The appearance of blood-borne AIDS was an instance of an awkward kind of uncertainty. Actors in the blood industry were not sure what was going on, and the available information was ambiguous. They constructed a set of standards, an information order, to evaluate information about the problem. Drawing on statements made to a commission of inquiry, as well as internal memos, minutes, and transcripts, I show that these standards were influenced by three factors: the external dependencies of these organizations, the exchange relations that bound them in di¡erent ways to their suppliers and recipients, and the organizational ties that linked them to other stakeholders in the blood industry.