On account of renewed interest in triple-stranded nucleic acid complexes we are carrying out a comprehensive thermodynamic study of helix formation among DNA homopolymers containing adenine, thymine and uracil. We have completed a calorimetric and spectroscopic study of the behavior of the poly(dA-poly(dT) system in the realm of high uni-univalent salt concentration where we have found the conditions for formation of a new polynucleotide complex and two entirely new helix-helix transformation reactions. The role and extent of displacement of cations, anions and water in these processes has been examined. The details of this work are being prepared for publication.