Historical accounts suggest that Jewish migrs from Nazi Germany revolutionized U.S. science. To analyze the migrs' effects on chemical innovation in the U.S. we compare changes in patenting by U.S. inventors in research fields of migrs with fields of other German chemists. Patenting by U.S. inventors increased by 31 percent in migr fields. Regressions that instrument for migr fields with pre-1933 fields of dismissed German chemists confirm a substantial increase in U.S. invention. Inventorlevel data indicate that migrs encouraged innovation by attracting new researchers to their fields, rather than by increasing the productivity of incumbent inventors.