In some ways, 1945 heralded a repeat of 1918. The world was exhausted after years of war and the Rockefeller Foundation was poised to make key investments in rebuilding science and medical research. However, as Gregg observed, there was a major difference: the federal government now was prepared to support clinical medicine, medical education, and research at levels that would soon far exceed the Rockefeller Foundation's pre-war funding. Unfortunately, as Gregg noted in 1950, the government had imitated the policies of the Rockefeller Foundation in making short-term research grants. As a result, Gregg made one last attempt to bring the foundation back to its former practice of awarding fewer grants of large size, with the goal of institutional development. "Only by doing what the Federal authorities can't do--e.g., long-term grants or endowments or special experiments in 'new' fields," Gregg argued, could the foundation avoid duplicating the work of a "far more powerful competitor." Moreover, with the Rockefeller Foundation's endowment funds, private institutions would be more independent of government funding and influence, which Gregg viewed as shortsighted and subject to political pressure.

Gregg's hopes were in vain, however. In addition to the trustees' reluctance, Gregg himself increasingly acknowledged the expanding influence of federal research funding. He saw this development firsthand, as he was invited to advise numerous government and private groups that hoped to tap these federal resources, which overshadowed those of the Rockefeller Foundation. Among the areas addressed by those boards or committees were the Atomic Energy Commission, medical education, socialized medicine, and the National Library of Medicine. Although Gregg knew that such groups also hoped he could help them tap the Rockefeller Foundation's resources, he agreed to participate when there was an important current or future issue about which he had expertise or wanted to learn. Gregg's method was usually to mobilize resources of both the private and government sector, and grant seed money for studies where necessary. An exception proving this rule was Rockefeller's support of sex research--notably that of Alfred Kinsey--where Gregg was willing to go it alone. Although funding went through the National Research Council, it was clear to all parties that the Rockefeller Foundation had to approve the funds for Kinsey's studies of human sexuality. In fact, Gregg visited Kinsey in Indiana and wrote the preface to his blockbuster bestseller, Sexuality in the Human Male; these actions demonstrated the extent to which Gregg was willing to acknowledge and defend the foundation's role in this controversial research.

Gregg was also called upon for his international expertise in the postwar period, most notably when he was asked to assess the postwar situation in China, where the Peking Union Medical College had suffered through the Japanese occupation, and then the effects of continuing civil war. Gregg headed a delegation to China in 1946, returning with a graphic report that prompted the trustees to cut their losses. In 1947, the foundation made a final grant of $10 million to the China Medical Board (an independent agency it had established in 1928 to support the Peking Union Medical College), almost doubling its endowment. In January 1951, the People's Republic of China nationalized the PUMC.

Gregg's "swan song" as the director of the Medical Sciences Division was a trip to India and Southeast Asia at the end of 1951. His detailed report of this visit, which addressed the future of medicine outside Europe and the Americas, echoed his early surveys of medical education. Although he knew that the foundation was unlikely to take concrete action, Gregg was primarily interested in demonstrating the model of a careful country survey to the new generation of Rockefeller officers.

Moreover, the India trip was part of Gregg's stepping down as head of the Medical Sciences Division to become a foundation Vice President, a position reflecting the role he had increasingly played after the war as a much sought after speaker at dedications, commencements, and dinners. Rather than hoping for Gregg's largesse, hosts sought the benefit of his observations on medicine, health, and philanthropy gained over thirty years of experience. This pattern continued even after his 1956 retirement. In fact, at the time of his death, Gregg was writing a memoir modestly titled "Notes on Giving."