Though he opposed communism, Szent-Györgyi welcomed the Russians as liberators when they arrived in early 1945. His heroic escapades during the war, along with his scientific fame, made him a notable public figure, and some believed he might become the first president of a democratic post-war Hungary, if the Soviets permitted a democracy to evolve. Szent-Györgyi visited Moscow several times with other Hungarian intellectuals, as part of a cultural exchange. Although the Soviet occupiers treated the general populace very badly, Szent-Györgyi was treated well, and given support for a laboratory at the University of Budapest, where he became professor of the biochemistry department. He also became a member of the reconstituted Parliament, and helped establish a new Academy of Sciences. Still, Soviet rule was gradually cutting Hungary off from the West again, and by 1946, Szent-Györgyi was quietly inquiring about appointments in the United States. The Massachusetts Institute of Technology offered him a temporary lectureship for spring of 1947, but Szent-Györgyi's visa was held up for nearly six months, apparently due to his cooperation with the Soviets and visits to Moscow. During the MIT appointment, Szent-Györgyi also renewed contact with the Rockefeller Foundation, in the hope of securing further funding. Shortly after he returned to Hungary, he again applied for entry to the United States. Again, the visa was held up for several months, but finally, in August 1947, Szent-Györgyi and his second wife, Marta, (he and Nelly had divorced in 1941) arrived in America.
Szent-Györgyi decided to settle at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, because he remembered the MBL (from his visit in 1929) as a place where he could rent lab space and work independently. A wealthy Hungarian friend, Stephen Rath, offered to fund a scientific foundation, including money to bring Szent-Györgyi's Hungarian research team over. The Szent-Györgyi Foundation was established as a non-profit corporation, with Rath handling the fund-raising and administration, and Szent-Györgyi directing the laboratory. The U.S. Office of Naval Research promised a generous research contract, once Szent-Györgyi assembled a research team, so Rath arranged to bring over six Hungarian colleagues during 1948. Nevertheless, funding proved a problem for several years; Rath's business dealings (with commercially interested backers) seemed rather shady to some academic scientists; and Szent-Györgyi was still being watched by the FBI because of previous "Communist associations." Further, most of his own money was in British banks and inaccessible until he established permanent U.S. residency. In 1949, to Szent-Györgyi's dismay, the Office of Naval Research withdrew its offer. Fortunately, he had obtained a research position at the National Institutes of Health in Bethesda in 1948, with provision for several Hungarian associates, and the Rockefeller Foundation provided a little additional grant funding. For several years, he and Marta shuttled between Woods Hole (where the Szent-Györgyi Foundation supported five or six research fellows with minimal salaries) and Bethesda. In 1950, Szent-Györgyi was saved by an offer from the Armour Meat Company, which agreed to support "fundamental studies in the field of muscle research" for up to five years. He also secured a grant from the American Heart Association. The Szent-Györgyi Foundation changed its name to The Institute for Muscle Research.
With funding once again coming in, Szent-Györgyi was able to gather a small group of talented researchers at Woods Hole and continue with his projects. Unlike most MBL scientists, Szent-Györgyi worked there year round, and he became a local legend of sorts. His research associates often stayed only a year or two before moving on to permanent academic posts, but they vividly recall the stimulating laboratory projects, Szent-Györgyi's freewheeling approach to science, and his warm hospitality. He and Marta often gave parties for the staff at their large house, Seven Winds, on Penzance Point, and hosted many visiting scientists during the busy summer season.
Szent-Györgyi and his group published steadily during this period. He summarized his work with muscle in a series of short, elegantly written books, which made him much better known among American scientists. Andrew Szent-Györgyi, Albert's younger cousin, and his wife Eva discovered the subunits of myosin ("meromyosins"), and began analyzing muscle proteins at a more elemental level. Szent-Györgyi and other colleagues did pioneering work analyzing muscle tissue with the electron microscope. In 1949, Szent-Györgyi also made another "tool box" discovery for muscle research, when he found that whole muscle tissue retained its contractility almost indefinitely if stored cold in a fifty percent glycerol solution, thus eliminating the need to have fresh muscle on hand. This work done during his first few years in the United States earned him a Lasker Award in 1954, one year before he became a U.S. citizen. In 1956, he was elected to the National Academy of Sciences. His congenial personality and colorful history made him popular with science writers, and he received hundreds of invitations to speak to various groups (which he almost never turned down).
In the late 1950s, Szent-Györgyi turned his attention to the problem of cancer. He began looking at chemical processes involved in growth, reasoning that cancer cells are characterized by abnormal growth patterns. He worked with thymus gland tissue for several years and extracted several substances, one that retarded growth ("retine") and another that promoted it ("promine.") Both seemed to be bioflavinoids. The substances were refined further, and experiments with animals and tissue cultures indicated that retine could produce regressions in some cancers. In the end, however, it proved impossible to isolate and identify retine and promine, and Szent-Györgyi realized that it would be foolish to propose them as cancer treatments without knowing their identities. This work did, however, start him thinking in terms of dynamic balances in nature, a concept which would guide his later investigations into free radicals, which continued to the end of his life. The deaths of his wife Marta and daughter Nelly from cancer during the 1960s provided additional impetus to his research.
The 1960s also rekindled Szent-Györgyi's interest in politics. Like many of his scientific colleagues, such as Linus Pauling and Salvador Luria, he was deeply concerned about the destructive uses of scientific knowledge, such as nuclear weapons, and about the dangers of militarism (evidenced by the Cold War and the war in Vietnam); he wrote a steady stream of articles and letters to the editor on the question of peace and survival, and published two books. His arguments often drew on western history, biology, and anthropology, and were notable for their broad philosophical qualities. Very sympathetic to the youth movement of the era, he proved an underground hero to the young people who crowded into Woods Hole each summer, and his MBL lectures were always well attended. Though he signed many petitions, gave many talks, and attended protest rallies, he did not found his own organization or movement, or formally join those organized by others.