In the beginning of the 20th century, German psychiatrists used pedigrees to disentangle the mechanisms underlying hereditary processes. Visualizing genealogical relations in a pedigree form served at least three ontologically distinct purposes. First, pedigrees were analytical devices which were supposed to bring to the fore certain regularities and thus facilitate the researcher’s ability to identify biological laws pertaining to the hereditary nature of mental illnesses. Second, pedigrees were used to document and communicate research results to peers in the scientific community. Finally, pedigrees were frequently reproduced and presented as part of an effort to propagate eugenic agendas to the German public. Using the same visual tool for different, not necessarily overlapping goals raises certain methodological problems. What assumptions were built into the formation of pedigrees when they were used as research devices? Was it legitimate to consider these assumptions as given when the same pedigrees were used as demonstrative aids? How were the conventions of pedigree-drawing affected by their simultaneous usage for inner-scientific and popular purposes? And how did contrasting political and academic views affect the visual choices psychiatrists were making when addressing genealogical data? The paper will survey the changes in the usage of pedigrees by German psychiatrists from 1900 to 1933 and analyze the different graphical choices in both the German and the international context of hereditary research at the time. Special attention will be given to the implicit and explicit assumptions built into certain graphical choices and to debates inside the scientific community regarding these issues. Pedigrees are not the only case in which visual tools are used simultaneously to satisfy different goals: the same holds true for graphs of all sorts (e.g., in economics). German psychiatry nonetheless will serve as a useful case-study, which would enable the examination of interactions between socio-political motivations and scientific interests as manifested in the visual domain of scientific work.