Because of the recent public concern over the brain drain, this study attempts to measure the U.S. gain of highly skilled manpower. The paper discusses the serious short‐comings of the data on gross immigration of scientists and engineers provided by the U.S. immigration authorities as a measure of true U.S. gains. In a case study of Swedish scientists and engineers it was found, for example, that whereas the U.S. data showed a gain of 106 Swedish scientists and engineers over a number of years, the net figure was only 26 after adjustment for remigration and the application of the proper OECD education criteria.The paper then reports the findings of a statistical study which uses the stock data on U.S. scientists in the National Register of Scientific and Technical Personnel to estimate the number of foreign born in this stock and analyse their characteristics with respect to age, educational attainment, and employment preferences.It was found that nearly 7 percent of all U.S. scientists are of foreign origin (foreign born and foreign secondary education), whereas 11.5 percent of all scientists with a Ph.D. are of foreign origin. The percentage among Ph.D. holders is highest in meteorology (22.3), followed by linguistics (18.7), physics (17.1) and statistics (14.6).The greatest percentage of scientists comes from Canada (10.4 per thousand), followed by Germany (8.3 per thousand) and the United Kingdom (6.7 per thousand). However, after adjustment of these data for the different sizes of the total foreign born population from each country in the U.S., it turns out that by this measure the greatest shares of scientists are supplied by the Japanese, followed by the Austrian‐Swiss, Benelux and Canadians.The analysis of the age composition of all foreign born reveals that in the age groups that were 20–29, 45–54, and 65 and over in 1964 foreigners represent a smaller than average share, probably reflecting war casualties and education completed at a later age. Germans and Austrians are heavily concentrated in the group 55–64 years old in 1964, suggesting that a great share of scientists from these countries may have been victims of a b