New hypotheses and predictions have arisen from recent work revealing atomic-scale or near-atomic-scale structures of receptors in the 'Cys-loop' superfamily. How general is the cation-pi interaction between the natural ligand and a tryptophan residue in the aromatic box, and does this interaction extend to other ligands? What is the pathway from the binding site to gating, and what are the conformational changes during gating and desensitization? Is current flow through intracellular 'portals' in the wall of the channel a general feature? This article discusses these and related questions, emphasizing nicotinic ACh receptors and also discussing data from other members of this superfamily.