Based on Hartree-Fock calculations we consider how changes in base-pair parameters affect the electronic coupling matrix element in DNA. The range of the parameters was determined using the statistical analysis of crystallographic data for DNA sequences. The electronic coupling is found to be very sensitive to intra base-pair deformations and its fluctuations can result in essential (several orders of magnitude) variation of the charge transfer rate. We conclude that structural distortions of nucleobase pairs significantly influence the electronic coupling in DNA pi-stacks and have to be accounted for by modeling of the hole transfer process and interpreting experimental findings. (c) 2006 Elsevier B.V. All rights reserved.