Abstract Using chiefly data published by the U.S. Immigration and Naturalization Service this paper presents a statistical summary of the trends in professional immigration into the United States. The proportion of immigrants who are professionals has been steadily increasing during recent decades, and change in immigration laws produced a sharper increase since 1965. The second trend of importance is the increasing proportion of professional immigrants who come from the less developed nations of the world. The effects of immigration on American science and medicine are discussed. Important benefits appear to have accrued to the U.S. The effects on the countries of origin are less beneficial. Finally, the reasons behind the migration of professionals are discussed.