Although many active scientists deplore the publicity about Drexler's futuristic scenario, I will argue that the controversies it has generated are very useful, at least in one respect. They help clarify the metaphysical assumptions underlying nanotechnologies, which may prove very helpful for understanding their public and cultural impact. Both Drexler and his opponents take inspiration from living systems, which they both describe as machines. However there is a striking contrast in their respective views of molecular machineries. This paper based on semipopular publications is an attempt to characterize the rival models of nanomachines and to disentangle the worldviews underpinning the uses of biological reference on both sides. Finally, in an effort to point out the historical roots... of the contrast in the concepts of nanomachines, I raise the question of a divide between two cultures of nanotechnology.