A new local information entropy (S ((r) over right arrow (HB))) has been defined based on Bader's theory of atoms in molecule using the electron density at hydrogen bond critical points (HBCPs). The local information entropy has been used to elucidate the stability and hydrogen bonding (H-bonding) interactions in DNA base pairs. The results reveal the usefulness of S ((R) over right arrow (HB)) in understanding the charge redistribution upon H-bonding and stability of various DNA base pairs. (c) 2005 Elsevier B.V. All rights reserved.