A combined density functional theory and Green's function procedure is used to calculate the electrical characteristics of Watson-Crick and non-Watson-Crick base pairs; calculations are performed to determine: the molecular orbitais that participate in the electron-transfer process, junction current-voltage characteristics, density of states, transmission function, and molecular electrostatic potentials. The distinct current-voltage features of base pairs can be used for detecting and sequencing DNA, as well as for detecting DNA base-pair mismatches by passing the double strand through two perpendicular metallic electrodes to the DNA, or by scanning the double strand with conducting probes. We find in the range from -1 to 1 V for the Watson-Crick pairs that the CG is a better electron conductor than the AT and, on the other hand, the best and worst conductors are the non-Watson-Crick mismatches CT and AA, respectively. © 2008 IEEE.