This method aims at providing structural information on protein or nucleoprotein complexes by high-resolution electron microscopy. The objective is to promote the self-assembly of the macromolecules into two-dimensional crystals in order to use electron crystallography methods. When combined with observations in the frozen hydrated states and dedicated image processing software these methods can provide detailed 3-D models of the complex. The 2-D crystals of soluble nucleoprotein complexes are formed on lipid monolayers spread at the air-water interface. The macromolecule of interest is targeted to the monolayer by either electrostatic or ligand-induced interactions with the hydrophilic head group of the lipid. Upon interaction with the lipids, the nucleoprotein complex is concentrated at the vicinity of the lipid layer whose in-plane mobility facilitates the contacts between macromolecules and the formation of ordered arrays.