Self-assembled aggregates of guanosine 5'-monophosphate (GMP) on the surface of muscovite mica were investigated by atomic force microscopy (AFM). Aqueous solutions of sodium, potassium and ammonium GMP salts were studied. For solution concentrations c < 0.005 wt% only small islands of deposited material are present on the surface. For c approximately 0.02 wt%, in addition to the islands and patches, also linear aggregates called G-wires are formed. The wire-like aggregates are on average 1.9 nm high and can be several micrometers long. They exhibit a profound directional growth along the six main crystallographic axes of the basal plane of mica. For c > 0.1 wt% flat terraces with the height of 2.5 nm appear. They are formed of G-wires lying with their long axis parallel to the substrate and stacking in a hexagonal arrangement. The morphology of the adsorbates is independent of the type of salt used to prepare the initial solution. This signifies that intrinsic potassium ions from the substrate play much more important role in the GMP adsorption than cations from the solution.