Influence of hydration on the Watson-Crick guanine-cytosine hydrogen bonded (h-bonded) base pair (GC) and stacked pair (G/C) was investigated in their first hydration shell. An electrostatic based approach has been used to identify the potential binding sites for water molecules around GC and G/C pairs. Several geometries of the complexes, GC...(H2O)(n) and G/C...(H2O), (n = 1-6) were investigated using HF/6-31G** and HF/6-31G++** methods. Further minimization calculations were performed at both B3P86/6-31G** and MP2/6-31G** levels to assess the role of electron correlation contribution in the hydration process. It can be concluded from the present findings that the stacked base-pair hydrate better than the corresponding h-bonded base pair, and DNA base pairs can accommodate up to 4-5 water molecules whereas stacked pair do accommodate 5-6 water molecules. (C) 2002 Elsevier Science B.V. All rights reserved.