Blood donation is often cited as a perfect example of altruism. But blood must be collected as well as donated, and the organizational basis of the blood supply has been largely neglected. This article is a comparative study of blood collection regimes in Europe. Regimes are found to affect donation rates and donor profiles. When the Red Cross collects blood, donation is tied to religious activity and other volunteering, unlike state and blood bank systems. This study argues that collection regimes produce their donor populations by providing differing opportunities for donations. The analysis contributes to an institutional perspective on altruism and highlights the need to attend to the socially embedded nature of altruistic as well as self?interested action.