Spin flip broken symmetry density functional theory is employed to determine the magnetic interactions in dehydrogenated Guanine-Cytosine (G-C) base pair. An antiferromagnetic (AFM) interaction between the electronic spins is suggested which gradually decreases at larger separation distances between the DNA bases. Beyond a certain separation distance, this AFM interaction becomes very weak and saturation in the values of magnetic coupling constant, J is observed. The variation in J values is in very good agreement with r (6) potential curve and also with the singlet-triplet energy gap. The overall investigation emphasizes the importance of H-bonding in determining the magnetic interactions in G-C diradicals. (C) 2008 Elsevier B.V. All rights reserved.