The average strength of hydrogen bonding interactions at the interface of 40 protein-DNA complexes comprising ~ 1500 potential hydrogen bonds and their free energies of formation have been estimated employing some recent advances in theoretical treatments of electrostatic interactions. The hydrogen bond spatial frequency distribution shows a maximum at a proton-acceptor distance of 2.1Å. The corresponding average interaction energy and the binding free energy are computed to be -1 kcal and +4 kcal/mol.H-bond respectively. Thus hydrogen bonds do not appear to provide the driving force for the formation of specific complexes from initially separated protein and DNA but serve to optimize the interactions in the specific complex once it is formed, via distance and angle requirements.