Theoretical ab initio calculations have been performed to determine the ability of the uracil-thymine (U.T) dimer to form stable covalent anions. The are two major conclusions of this work (i) Two isomeric structures of the covalent U.T dimer have been found in the calculations. The anion, where the excess electron is located at the uracil molecule, is 1.4 kcal/mol more stable than the form where the excess electron is located at the thymine molecule. (ii) The ring of the molecule where the excess electron is localized in noticeably nonplanar.