McClintock's work on chromosomal crossing-over strengthened her early reputation in cytogenetics. During the early 1930s, McClintock received two fellowships to travel and conduct research. The first of these was a two-year postdoctoral fellowship from the National Research Council, which supported her research at Cornell and, later, at the University of Missouri at Columbia and at the California Institute of Technology. During the summers of 1931 and 1932 at Missouri, McClintock had the opportunity to work with Lewis Stadler, a leading maize cytogeneticist in the United States at the time, who introduced her to the use of X-rays as a tool for studying genetics.
In 1933, McClintock received a prestigious Guggenheim fellowship to study in Berlin with the noted German geneticist Curt Stern. The rise to power of Adolph Hitler and the Nazi Party, however, forced many Jewish scientists like Stern to abandon their work in Germany and find positions at institutions in England, France, and the United States. Despite the absence of her colleague, McClintock traveled to Berlin and instead encountered the important German geneticist Richard B. Goldschmidt, the head of the Kaiser Wilhelm Institute in Berlin. At Goldschmidt's suggestion, McClintock relocated to the Botanical Institute in Freiburg. She returned to Cornell in April 1934, dispirited from her experiences in Germany, although she learned a great deal while traveling abroad. In December 1934, reflecting on her time in Germany, she wrote to Stern, "I couldn't have picked a worse time. The general morale of the scientific worker was anything but encouraging. There were almost no students from other countries. The political situation and its devastating results were too prominent."