Ernst Rüdin (1874-1952), director of the Deutsche Forschungsanstalt für Psychiatrie in Munich, was one of the leading psychiatrists in Nazi Germany. Prevailing historical research on Rüdin's relation to the systematic annihilation of psychiatric patients is dominated by the only hitherto available biographical account which suggests that Rüdin privately disapproved of the "euthanasia" program, but did not make this disapproval public. According to this account, neither Rüdin nor any of his co-scientists were in any way actively involved in the systematic killings. In contrast to this image, a general evaluation of the historical sources on the systematic killing of patients clearly shows that due to the fragmentary character of the evidence, any exculpation of particular individuals or institutions is premature to date. Furthermore, the reevaluation of already known archival material and new documents presented here proves that Rüdin had a genuine interest in research which on the one hand made profitable use of the killings, and on the other hand was aimed at formulating scientific criteria for the systematic selection and "euthanasia" of those supposedly unworthy to live. Julius Deussen (1906-1970), since 1939 head of the department for hereditary psychology at the Deutsche Forschungsanstalt, was also a close co-worker of Carl Schneider (1891-1946) at the University of Heidelberg. He coordinated the research on children carried through in the context of the "euthanasia"-programme between 1943 and 1945. This research sought to systematically correlate clinical and laboratory findings with the histopathological data of the victims' brains. From the beginning, it included the killing of the patients. Central elements of the research programme had been formulated by Deussen already in Munich. Rüdin supported the activities of Deussen in Heidelberg and repeatedly pointed out that they were of importance for the health and population policy of the Nazi regime.