The Tuskegee syphilis experiment was an infamous clinical study conducted between 1932 and 1972 in Tuskegee, Alabama by the U.S. Public Health Service to study the natural progression of untreated syphilis in rural black men who thought they were receiving free health care from the U.S. government.
The Public Health Service, working with the Tuskegee Institute, began the study in 1932. Investigators enrolled in the study a total of 600 impoverished sharecroppers from Macon County, Alabama; 399 who had previously contracted syphilis before the study began, and 201 without the disease. For participating in the study, the men were given free medical care, meals, and free burial insurance. They were never told they had syphilis, nor were they ever treated for it. According to the Centers for Disease Control, the men were told they were being treated for "bad blood", a local term for various illnesses that include syphilis, anemia, and fatigue.
The 40-year study was controversial for reasons related to ethical standards; primarily because researchers knowingly failed to treat patients appropriately after the 1940s validation of penicillin as an effective cure for the disease they were studying. Revelation of study failures by a whistleblower led to major changes in U.S. law and regulation on the protection of participants in clinical studies. Now studies require informed consent (with exceptions possible for U.S. Federal agencies which can be kept secret by Executive Order), [not in citation given] communication of diagnosis, and accurate reporting of test results.
By 1947, penicillin had become the standard treatment for syphilis. Choices available to the doctors involved in the study might have included treating all syphilitic subjects and closing the study, or splitting off a control group for testing with penicillin. Instead, the Tuskegee scientists continued the study without treating any participants and withholding penicillin and information about it from the patients. In addition, scientists prevented participants from accessing syphilis treatment programs available to others in the area. The study continued, under numerous US Public Health Service supervisors, until 1972, when a leak to the press eventually resulted in its termination on November 16. The victims of the study included numerous men who died of syphilis, wives who contracted the disease, and children born with congenital syphilis.
The Tuskegee Syphilis Study, cited as "arguably the most infamous biomedical research study in U.S. history,"led to the 1979 Belmont Report and the establishment of the Office for Human Research Protections (OHRP). It also led to federal laws and regulations requiring Institutional Review Boards for the protection of human subjects in studies involving human subjects. The Office for Human Research Protections (OHRP) manages this responsibility within the US Department of Health and Human Services (HHS).

In 1974 Congress passed the National Research Act and created a commission to study and write regulations governing studies involving human participants. On May 16, 1997, President Bill Clinton formally apologized and held a ceremony for the Tuskegee study participants: "What was done cannot be undone. But we can end the silence. We can stop turning our heads away. We can look at you in the eye and finally say on behalf of the American people, what the United States government did was shameful, and I am sorry ... To our African American citizens, I am sorry that your federal government orchestrated a study so clearly racist." Five of the eight remaining study survivors attended the White House ceremony.

The Tuskegee Syphilis Study significantly damaged the trust of the black community toward public health efforts in the United States. As a result, many distrust the medical community and are reluctant to participate in programs such as organ donation. The study may also have contributed to the reluctance of many poor black people to seek routine preventive care. However, recent studies have challenged the degree to which knowledge of the Tuskegee experiments have kept black Americans from participating in medical research. Distrust of the government because of the study contributed to persistent rumors in the black community that the government was responsible for the HIV/AIDS crisis by introducing the virus to the black community.