The SS also interned recidivist criminals, Jehovah's Witnesses, Roma and Sinti (Gypsies), and German military deserters at Buchenwald. Buchenwald was one of the only concentration camps that held so-called “work-shy” individuals, persons whom the regime incarcerated as “asocials” because they could not, or would not, find gainful employment. In the camp's later stages, the SS also incarcerated prisoners-of-war of various nations (including the United States), resistance fighters, prominent former government officials of German-occupied countries, and foreign forced laborers.

Beginning in 1941, a number of physicians and scientists carried out a varied program of medical experimentation on prisoners at Buchenwald in special barracks in the northern part of the main camp. Medical experiments aimed at testing the efficacy of vaccines and treatments against contagious diseases such as typhus, typhoid, cholera, and diphtheria resulted in hundreds of deaths. In 1944, Danish physician Dr. Carl Vaernet began a series of experiments that he claimed would "cure" homosexual inmates through hormonal transplants.