The injections of plutonium and other radioactive substances during the Manhattan Project represent one of the most troubling ethical violations in medical research history. These tests were carried out just after World War II, between 1945 and 1947, in hospitals linked to the Manhattan Project in Rochester, Chicago, San Francisco, and Oak Ridge. The main goal was to understand how plutonium behaved inside the human body to enhance safety protocols for workers involved in producing nuclear materials. Unfortunately, this research came at a great human cost, as many patients were not informed nor did they consent to receive such injections. These patients included vulnerable individuals, many terminally ill, who were subjected to experimental procedures not meant to treat or benefit them directly but rather to protect military and industrial personnel. The lack of informed consent contradicts modern ethical standards established later by documents such as the Nuremberg Code and the Declaration of Helsinki. This case highlights the critical importance of respecting patient autonomy and the necessity of transparent informed consent in any research involving human subjects. Furthermore, these experiments reveal how national security and scientific advancement were often prioritized over individual rights during the Cold War era. The acknowledgment of such experiments has fueled significant debate around government transparency, medical ethics, and the protection of human subjects. It also serves as a reminder to ensure rigorous oversight and ethical review in all clinical trials today. While some details of the experiments were initially hidden or downplayed, public awareness has grown through declassified documents and historical research. Understanding this dark chapter helps contextualize the ongoing discussions about ethical conduct in science, and the need to carefully balance scientific progress with human dignity and justice.