Dynamic light scattering in the pretransitional region of the I --> Ch phase transition of deoxyguanosine 5 ' -monophosphate reveals the presence of two diffusive modes. The slower made is assigned to the translational motion of large spherical aggregates, similar to those observed in isotropic solutions of DNA and other polyelectrolytes. The faster mode is assigned to the translational motion of stacked arrays of guanosine tetramers and can be described by the polyion diffusion.