In comparison to other biomolecules, the effect of hydrostatic pressure on the conformational stability of DNA and RNA has received scant attention. However, the increasing interest in the hydration of biological molecules has resulted in a concomitant increase in the number of investigations of the effect of pressure upon the structure of nucleic acids. In this review, studies concerning the effect of pressure on DNA and RNA oligomers and polymers are presented. The greatest amount of research has been directed at studying the effect of pressure on the stability of the double helix. In general, under most conditions, the helical form of DNA or RNA is stabilized by pressure. The extent of stabilization is small relative to the effect of pressure on other biomolecular systems such as lipid membranes or protein quaternary structure. The absence of a larger pressure effect arises, in part because the state of ionization does not change as a function of the helical state. Initial experiments have also appeared on the effect of pressure upon helixformation kinetics, B-Z and A-Z equilibria, and DNA topology. Fourier-transform ir spectroscopy of DNA polymers under high pressure has yielded data that showing that pressure does not induce large-scale structural changes.