Gold and other metals spontaneously and dramatically change their known properties if reduced in size to the nanometre scale. The classical physical laws for macroscopic metals are then no longer valid, but quantum mechanical rules, especially reflected by the formation of discrete electronic energy levels instead of the three-dimensional electron gas in bulk metals. From this, completely novel applications follow, representing a significant part of current nanosciences. From a biological point of view, it is important to note that gold nanoparticles are far from being as inert as has been expected for a long time. On the contrary: on the nanometre scale gold has the ability to interact with DNA. Moreover, gold nanoparticles show pronounced size-dependent cell toxicity by inducing the formation of intracellular reactive oxygen species which damage the mitochondria. As a consequence, the energy metabolism in the cell collapses, leading to a fast cell-death by necrosis. The question whether gold nanoparticles can be used in tumour therapy cannot be conclusively answered. For sure, a better tumour targeting will be necessary that could be reached for example by using ligands modified by “anchor molecules”. By proving the toxicity of Au 1.4 MS, numerous questions can be asked. For instance, it should be investigated which effects will occur by inhalation in order to be able to evaluate them in the present fine-dust discussion.