Electrostatic potential maps for the 10 Watson-Crick base-pair combinations of dinucleoside monophosphates in a conformation appropriate for intercalation of drugs to occur are presented. These maps reveal interesting differences among the base-pair combinations and suggest reasons for the base-pair specificities often observed upon intercalation. Simple electrostatic calculations on the intercalation energy of substituted actinomycin chromophores correlate qualitatively with the relative biological activity of these compounds, although the correlation with binding affintiy is not as satisfactory.