Historically, the disease was studied under the Tuskegee study, a notable example of unethical human experimentation. The study was done on approximately 400 African-American men with untreated syphilis who were followed from 1932 to 1972 and compared to approximately 200 men without syphilis. The study began without informed consent of the subjects and was continued by the United States Public Health Service until 1972. The researchers failed to notify and withheld treatment for patients despite knowing penicillin was found as an effective cure for neurosyphilis. After four years of follow up, neurosyphilis was identified in 26.1% of patients vs. 2.5% of controls. After 20 years of followup, 14% showed signs of neurosyphilis and 40% had died from other causes.