Hugh Auchincloss, Jr. (/ˈɔːkɪnklɒs/ AW-kin-kloss; born March 15, 1949) is an American immunologist and physician who served as the acting director of the National Institute of Allergy and Infectious Diseases from January to August 2023.

Prior to government service, Auchincloss was a transplant surgeon and full professor of surgery at Harvard Medical School, and researched at Massachusetts General Hospital for 17 years.

His mother was the daughter of lawyer Harvey Hollister Bundy, and the granddaughter of banker William Lowell Putnam.

[6] In 2006, he joined the National Institute of Allergy and Infectious Diseases (NIAID) as the principal deputy director.

[8] Emails between Dr. Anthony Fauci and Auchincloss regarding NIAID involvement in gain-of-function research and the COVID-19 pandemic were featured during a hearing of the Republican House Energy and Commerce Committee on 2 June 2021.

[6] Auchincloss is on federal and NIH-wide committees, including the Trans-Federal Task Force on Optimizing Biocontainment Oversight, the National Security Strategy/Office of Science and Technology Policy on Optimizing Biological Select Agents and Toxins Working Group, and the National Biodefense Science Board.