This paper examines the US Atomic Energy Commission's radioisotope distribution program, established in 1946, which employed the uranium piles built for the wartime bomb project to produce specific radioisotopes for use in scientific investigation and medical therapy. As soon as the program was announced, requests from researchers began pouring into the Commission's office. During the first year of the program alone over 1000 radioisotope shipments were sent out. The numerous requests that came from scientists outside the United States, however, sparked (...) a political debate about whether the Commission should or even could export radioisotopes. This controversy manifested the tension between the aims of the Marshall Plan and growing US national security concerns after World War II. Proponents of international circulation of radioisotopes emphasized the political and scientific value of collaborating with European scientists, especially biomedical researchers. In the end, radioisotopes were shipped from the Commission's Oak Ridge facility to many laboratories in England and continental Europe, where they were used in biochemical research on animals, plants, and microbes. However, the issue of radioisotope export continued to draw political fire in the United States, even after the establishment of national atomic energy facilities elsewhere. (shrink)