A link between scanning tunneling microscopy (STM) and conventional transmission electron microscopy (TEM) has been established by applying STM on freeze-dried recA-DNA complexes coated with a conducting film. The direct observed three-dimensional topography reveals right-handed single-helix pitch and recA monomers without any averaging. The STM is also able to resolve structural, physical and chemical features of bare airdried recA-DNA complexes.