Long-range interactions in the beta-sheet structure of oligoglycines Gly(n) (n = 2-10) have been investigated by DFT computations using the B3LYP exchange-correlation functional in conjunction with a diffuse polarized valence triple-xi basis set. The study focused on the evaluation of the title interactions in the Gly(n) chain and on the quantitative determination of their consequences in both energy and geometry. It was found that the interactions contribute considerably to the stability of the beta-sheet and have a substantial impact on the geometrical parameters. On the basis of the gradual build-up of energetic and geometrical effects, we determined the effective radius of long-range interactions to be around 10 Gly units in the beta-sheet Gly(n). The energy gain from the long-range interactions of a Gly unit is around 2.5 kJ/mol, stemming to a large extent from the strengthening of the N-(HO)-O-...=C hydrogen bonds. Among the geometrical parameters, the (HO)-O-... hydrogen-bond length is the most sensitive to long-range effects, decreasing by several hundredths of an angstrom. Besides, there is a pronounced shortening of the C-N bonds (up to 0.009 Angstrom), while the other bond distances vary within 0.002 Angstrom and the bond angles within 0.5degrees. Our structure analysis revealed also a small (a few thousands of an angstrom) elongation versus contraction of the chain depending on the parallel versus antiparallel orientation of the NH2 and COOH end-dipoles. The alterations of the bond distances upon long-range effects are associated with appreciable changes in the magnitude of the main hyperconjugation interactions.