Tôn Thất Tùng was a key player in the effort to counter biological warfare during the First Indochina War. In July 1951, he traveled to China and North Korea. Upon arrived in Beijing on July 28, he proceeded to carry out both political and medical exchanges. Tùng next visited the Democratic People's Republic of Korea. In August 1951, the fighting on the Korean peninsula was intense and Tùng witnessed the regular bombings of Pyongyang. He noted in his diary how the residents of Pyongyang had come to know the schedule of what he called 'American' bombs. Tùng's observations of life in North Korea were eerily similar to later accounts of life in Hanoi during the US bombings of the 1960s.
Tùng left China at the end of 1951 before the charges of US germ warfare surfaced. Moreover, his training as a surgeon would not have shed much light on biological weapons. He did, however, serve as the chair at the first meeting of the Committee to Prevent Germs (Ban Chống Trùng or BCT) held from September 12 through 16, 1952.
At the battle of Điện Biên Phủ in 1954, which effectively ended the First Indochina War, Tùng directed much of the field surgery. He also kept a diary covering his experiences there. In his entry for April 26, Tùng recounted possible incidents of weather modification and the release of worm-infested leaflets. He also frequently discussed the sight and sound of airplanes and specifically mentioned the US-made Hellcat and B-26 (Tùng Journal 1954).
Tùng's experience with allegations of biological warfare in the early 1950s helped frame his subsequent study of chemical herbicides, including Agent Orange, used by the American and South Vietnamese militaries from 1961 to 1970. By that time Tùng had largely stopped his surgery practice but he continued an active research program into the possible effects of herbicides on present and future generations of North Vietnamese. Tùng maintained a wide network of colleagues and friends, including Jean-Michel Krivine, a French surgeon and communist party member. Tùng recognized the limited resources at his disposal within the DRV and he used his network to gather any information he could about the consequences of herbicide exposure.