Unlike their fellow Brazilians, social scientists in Europe and North America paid close attention to issues of blood donation and policy many years before the AIDS pandemic. This article is partly an attempt to review such pioneering studies. Among the most important contributions from the social sciences was Richard M. Titmuss's path-breaking study on The Gift Relationship (with the subtitle From Human Blood to Social Policy), published in England in 1971. Based on a 1967 survey of blood donors in England and on comparable data from other developed countries, it is a classic study of moral philosophy and public policy. Through this book, Titmuss became known as a staunch supporter of voluntary, non-paid donations, which, in his view, contributed to decrease the risks of transfusion-related hepatitis, and, most important, helped promote altruistic behavior within the social systems. This paper summarizes Titmuss's ideas and policy proposals, and discusses some authors who, in subsequent years, endorsed both his ideas and policy recommendations. From an opposite battle field (in American soil), the article selects two representative papers by Kenneth Arrow and Harvey Sapolsky, who diligently attempt to criticize Titmuss's views. The authors present a different, neoliberal set of principies in support of a free market for blood and plasma, where paid donations for whole blood and plasma collection must be allowed. Harvey Sapolsky, in particular, argues that the creation of paneis of paid, carefully monitored, blood donors may actually decrease the risks of contamination from hepatitis or AIDS. According to Sapolsky, Titmuss failed to see that the links between voluntary donations and transfusion-related hepatitis are unclear, and that even his 1967 survey data do not suggest the existence of any clear-cut relationship. For this reason, writes Sapolsky, it is also misleading to expect that unpaid donations will protect against AIDS. As the present paper tries to show, Sapolsky's analysis and proposals deserve careful consideration. They seem to represent a perfect case for an old dictum on "the creative power of the erroneous idea." His policy proposals seem perfectly sound, yet his moral philosophy - as much as Arrow's - is less convincing and enticing than Titmuss's. A related purpose of the article is to take some lessons from the international literature. In what ways are the various arguments on blood and social policy, summarized in the present article, relevant to the Brazilian debate? Unfortunately, petty politics and parochial interests have dominated the debate in Brazil, particularly in the Congress. In hopes that the Congress may be pressed to consider the real interests of the population in the future, this paper wishes to attract the attention of the professional groups and social movements involved in the fight against transfusion-related AIDS (which only 3 years ago accounted for 8% cases of the disease) to the technical and organizational issues discussed in the international literature. Specifically. the paper attempts to contribute to the current effort of revision of the legislation approved by the 1988 Constitution Assembly, which completely ignored crucial issues on the nature and operation of blood systems, such as those raised in the Titmuss-Arrow controversy.