Controlling DNA adsorption to atomically fiat surfaces is crucial for studying protein-DNA interactions with the atomic force microscope (AFM). We present a method that enables reversible binding of this molecule to mica during AFM imaging in liquids. This can be acheived using a flow-through system which allows the exchange of different buffers that promote and inhibit the DNA adhesion to the surface. The DNA adsorption is controlled primarily through the divalent cation concentration. The DNA visibility in the AFM was investigated as a function of pH and cation concentration.