The participants were not informed of all the known dangers.
The participants had to agree to an autopsy after their death, in order to have their funeral costs covered.
Scientists denied treatment to some patients, in order to observe the individual dangers and fatal progression of the disease.
Participants were not given the cure, even when it was widely known and easily available.
The designers used a misleading advertisement: The researchers advertised for participants with the slogan; "Last Chance for Special Free Treatment". The subjects were NOT given a treatment, instead being recruited for a very risky spinal tap-diagnostic.
At the beginning of the study, the subjects were not well informed about the whole purpose of the research; neither were they informed of the inherent dangers of the study. The experiment was at the time seen as potentially beneficial for the humankind, but did not consider the harm caused to individuals and their families.
By 1947, Penicillin had become the standard treatment for curing syphilis. Instead of performing the necessary duty; closing the study and giving all of the subjects some penicillin, the scientists of Tuskegee Syphilis Study withheld treatment from many of the participants. The scientists did not follow the commonly used ethical rules of research.
The study ended in 1972, 25 years after the cure was known and publicly available.
By the end of the study, 28 persons had died from the disease, 100 persons had died from related diseases and 40 wives and 19 children had been infected with syphilis.