This paper provides some general views on the current guidelines on the purity of medicinal products, with the purpose of informing the medicinal industry about the Danish Medicines Agency's view on how to establish requirements on impurities in chemically-synthesised active substances (the Danish Medicine Agency's rules of thumb do not cover nonchemical substances) and medicinal products for human use. It should be emphasized that the points of views represent the Danish Medicines Agency's interpretation of the quality guidelines in question.