The formation of Pd nanoparticles on crystalline bacterial cell surface layers has been studied by means of electron microscopy and the small-angle scattering of X-rays (see figure) and neutrons. The response of the S-layer lattice to the loading with Pd complexes and metallic Pd particles as well as the effects of two different reducing agents (H and dimethylaminoborane) on the observed nanoparticle arrays are described.