The chemical and magnetic structures of neodymium/praseodymium superlattices grown by molecular-beam epitaxy have been determined using x-ray and neutron-diffraction techniques. The x-ray measurements show that the superlattices have a dhcp structure of high crystalline quality, and that the stacking sequence is coherent over many bilayer repeats. The neutron measurements show that for the hexagonal sites of the dhcp structure, the Nd magnetic order propagates coherently through the Pr, whereas the order on the cubic sites is either suppressed or confined to single Nd blocks. It is also shown that the singlet ground state of Pr is perturbed to produce a local moment on the hexagonal sites, so that in some cases there is a uniform magnetic structure throughout the superlattice. These results cast new light on the theory of magnetic interactions in rare-earth superlattices. Within a few months of growth these light rare-earth samples are found to react with hydrogen to form new single-crystal phases, which are coherent with the epitaxial structure.