Imperial Japanese Army Medical School Site

The Imperial Japanese Army Medical School (陸軍軍医学校, Rikugun Gun'i Gakkō) was the premier military medical training institution of the Japanese Empire. Originally established on May 21, 1886 under the Army Medical School Outline Regulations (陸軍軍医学舎概則), the school initially operated within the Army Ministry headquarters in Tokyo's Nagatachō district. In December 1888, it was formally restructured as the "Army Medical School" (陸軍軍医学校) by Imperial Decree No. 97. The school had relocated in January 1888 to Fujimi-chō in Kōjimachi Ward (now Chiyoda Ward), and in 1929 moved to a large campus in Toyama, Ushigome Ward (now Toyama, Shinjuku Ward), adjacent to the Army Toyama School firing range and the Owari Tokugawa clan's former estate grounds.

The Toyama campus became one of the most significant military medical research complexes in Asia. It housed multiple departments including surgery, internal medicine, hygiene, pharmacology, pathology, and — most notoriously — the Epidemic Prevention Research Laboratory (防疫研究室, Bōeki Kenkyūshitsu), established in 1932 under the direction of Army Surgeon Major Shirō Ishii (石井四郎). Ishii, a graduate of Kyoto Imperial University's medical faculty and an ambitious military physician, had traveled to Europe in 1928–1930 to study biological weapons and returned convinced that Japan needed an offensive biological warfare capability. The Epidemic Prevention Research Laboratory became the Tokyo command center for a network of biological warfare units, most infamously the Kwantung Army Epidemic Prevention and Water Purification Department — better known as Unit 731 (第731部隊) — headquartered at Pingfang near Harbin, Manchuria.

From the Toyama campus, Ishii coordinated a vast apparatus of human experimentation and biological weapons development. Unit 731 and its subordinate units conducted lethal experiments on thousands of prisoners (referred to by the euphemism "maruta" / 丸太 / logs), including deliberate infection with plague, cholera, typhus, anthrax, and other pathogens; live vivisection without anesthesia; frostbite experiments; pressure-chamber tests; and weaponized pathogen dispersal trials. The Toyama facility itself housed research specimens, pathological materials, and served as the administrative hub connecting the field laboratories in Manchuria, China, and Southeast Asia to the Army General Staff in Tokyo.

Other biological warfare units operating under the Army Medical School's umbrella included Unit 100 (関東軍軍馬防疫廠) in Changchun, specializing in animal and crop pathogens; Unit 516 in Qiqihar, developing chemical weapons; Unit 1644 in Nanjing; and Unit 8604 in Guangzhou. The total number of victims across these programs is estimated at between 3,000 and 12,000, though the true figure may never be known due to systematic destruction of records at war's end.

In August 1945, as Soviet forces invaded Manchuria, Ishii ordered the destruction of the Pingfang facility, the killing of remaining prisoners, and the repatriation of staff to Japan. Most records were burned. After Japan's surrender, Ishii and other Unit 731 leaders struck a secret deal with the United States: in exchange for sharing their biological warfare research data, they received immunity from prosecution as war criminals. This arrangement, authorized by General Douglas MacArthur's headquarters, remained classified for decades.

After the war, the Toyama campus was transferred to the Ministry of Health and Welfare. The adjacent Tokyo First Army Hospital became the National Tokyo First Hospital, eventually becoming the National Center for Global Health and Medicine (国立国際医療研究センター) in 2010, while the school grounds themselves came to house the National Institute of Nutrition (from 1948) and, from 1992, the National Institute of Infectious Diseases (国立感染症研究所, formerly the National Institute of Preventive Health). In April 2025 the two institutions were merged into the Japan Institute for Health Security (国立健康危機管理研究機構).

On July 22, 1989, during construction of a new building for the National Institute of Preventive Health on the former Army Medical School grounds, workers discovered a large quantity of human bones buried approximately 2 meters below the surface. Initial police examination identified skulls and femur bones from an estimated 35 individuals. In 1992, a comprehensive anthropological analysis by Professor Hajime Sakura of Sapporo Gakuin University determined that the remains came from at least 62 — and possibly more than 100 — individuals. The analysis revealed several disturbing findings: the remains were predominantly adult, comprising multiple Asian ethnic groups including individuals likely of non-Japanese origin; numerous skulls exhibited evidence of artificial processing including drilling, sawing, and surgical cutting consistent with trepanation or mastoidectomy procedures; some bore traces of gunshot wounds and blade incisions; and several showed signs of chemical preservation.

The discovery triggered intense public debate and demands for investigation. In 2001, the Ministry of Health, Labour and Welfare released a report acknowledging the bones were "specimens or remains collected for specimen preparation or medical education" from the Army Medical School era, and that "some may have included materials derived from war dead collected from battlefields." However, the ministry declined to confirm any direct connection to Unit 731. Citizens' groups, historians, and Chinese organizations have persistently argued that the evidence — including the ethnic diversity of the remains, the surgical marks, and the site's direct institutional link to Ishii's laboratory — points to victims of biological warfare experimentation. In February 2011, the ministry began its first excavation of its own, on the nearby site of a former ministry housing block. The recovered remains are currently stored in an ossuary within the National Institute of Infectious Diseases grounds, their identities still officially unknown.

The site carries no prominent memorial or historical marker acknowledging its wartime role. Toyama Park (戸山公園), which occupies the former Army Toyama School grounds immediately adjacent, contains no reference to the biological warfare program. The National Institute of Infectious Diseases and the neighbouring medical center — the latter dedicated to international health cooperation — operate on and beside land where some of the twentieth century's most egregious medical atrocities were planned and coordinated.