This chapter examines the implications of the "natural' and the "unnatural' for human enhancement and doping. In public discussions, the natural often seems to have a moral bonus. However, this bonus is far from self-evident, because the natural can be seen as morally neutral and has positive as well as negative consequences for human life circumstances. In the case of human beings, it is also difficult to define, what their actual nature is, because humans are in general the source of the artificial and the cultural sphere. In the article, three different meanings of the natural are distinguished and analysed in the context of doping and enhancement measurements. With reference to Boorse's naturalistic approach, it is shown, that the "normal' state of the human body (in the sense of Boorse's theory) in contrast to non-therapeutic body modifications can indeed have some normative implications, i.e. that doping interventions which interfere with the body's natural state may be dangerous and therefore also unethical regarding the interests of the concerned person.