 Upon returning to the U.S. during World War II, he took a position at Yale University's Connecticut Agricultural Experiment Station to work with Hubert Bradford Vickery.He joined the lab of eminent protein chemist Max Bergmann at the Rockefeller Institute in 1940, where he worked with a number of important biochemists and began a significant line of research on the intestinal enzyme erepsin.Between 1942 and 1946, he worked at E. R. Squibb & Sons on the production of human blood products for use in the war.