The charge of complicity has been raised in debates over the ethics of fetal tissue transplantation and embryonic stem cell research. However, the applicability of the concept of complicity to these types of research is neither clear nor uncontroversial. This article discusses the historical case of Julius Hallervorden, a distinguished German neuropathologist who conducted research on brains of mentally handicapped patients killed in the context of the Nazi ‘euthanasia’ programme. It is argued that this case constitutes a paradigm of complicity (...) in research that is useful in assessing complicity in contemporary research ethics. (shrink)