Temperature dependence of the self-assembling properties of aqueous solutions of deoxy- and guanosine 5'-monophospate (dGMP and GMP) in the pretransitional region of the I-Ch phase transition was investigated by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). The dGMP molecules start to assemble at lower concentrations and form considerably longer aggregates than GMP molecules. Conversely, the aggregate melting curves of both derivatives are very similar and show three characteristic regions: a low temperature interaction-controlled region, a narrow region of intense aggregate dissociation, and a high temperature region of dissociated species.