The nature of DNA adsorption to various substrates has been investigated by atomic force microscopy. The substrates used were mica, silylated mica, calcite, fluorite, and barite. The presence of a divalent cation, either in solution or accessible to the DNA on the substrate, greatly improves DNA adsorption. A comparison of DNA adsorption from different buffers onto mica and silylated mica shows that buffer composition is much less important for DNA adsorption to silylated mica and also suggests that for good adsorption DNA must be electrostatically adsorbed to the surface.