The largest flow of scientific talent in the world is the migration of international students to universities in industrialized countries. We use the opening of China in 1978 to estimate this flow's causal effect on the productivity of their professors in the United States. Our identification relies on both the suddenness of China's opening and on a key feature of scientific production: intra-ethnic collaboration. The increased access that Chinese-American advisors had to a new talent pool led to an increase in their productivity, in both coauthorships and solo-authored papers. Comparable non-Chinese advisors mentored fewer non-Chinese students and published fewer papers.