Under his politically understated guidance, and in the face of continued political opposition from Mississippi Governor Ross Barnett, his administration admitted the first African-American medical students, hired the first black medical professor, integrated the medical center's patients, and set new precedents for the non-violent racial desegregation of Southern medical schools and teaching hospitals. Later, in 1965, he was chosen to be the university's vice-chancellor. He rejoined the NIH in 1966, first as NIH associate director and the director of the fledgling Regional Medical Programs Division, charged with cancer, heart disease and stroke research. Then, during an April 1968 internal reorganization of NIH, he was selected to be the new administrator of the Health Services and Mental Health Administration. Only five months later, in September, Marston was chosen to be the NIH director. During his last year as the NIH director, Marston became embroiled in a funding controversy with the Nixon administration, which wanted to place greater funding emphasis on a "war on cancer." Marston believed that emphasizing one disease at the expense of other medical research was bad policy, and continued to support balanced, comprehensive funding priorities. He eventually resigned from NIH in April 1973, after nearly five years as director. Afterward, he became a scholar-in-residence at the University of Virginia in Charlottesville, Virginia. The National Academy of Sciences' Institute of Medicine named him as its inaugural distinguished fellow. In 1974, the Florida Board of Regents chose Marston as the seventh president of the University of Florida located in Gainesville, Florida; he undertook the presidency during a time of economic recession, state budget cuts and increased demand for private funding of the university. During his ten-year tenure, the university matured into one of the United States' ten largest single-campus universities and one of the five most inclusive in the scope of its academic programs, with significant growth in its sponsored research activities, and notable advancement of the university's academic excellence and reputation. Marston's accomplishments as university president included the organization of a non-profit corporate structure for the management of Shands Hospital, helping establish the State of Florida's Eminent Scholars Program, dramatically increasing the university's private financial support, developing plans to recruit National Merit Scholars and National Achievement Scholars, and laying the organizational foundation for the University of Florida's eventual membership in the Association of American Universities (AAU). After retiring as the University of Florida president emeritus in 1984, Marston returned