Viscosity, g and enthalpy of dilution, q of studied nucleic acid bases (uracil, cytosine, thymine) and nucleosides (uridine, cytidine and thymidine) in water and in aqueous solutions of (0.10, 0.25, 0.50, 0.75 and 1.00) mol.kg(-1) guanidine hydrochloride (GnHCl) have been determined over a temperature range (288.15-318.15) K at (101.3 +/- 0.5) kPa. These data have been used to calculate viscosity B-coefficients and standard molar enthalpy of dilution, Delta H-dil(o) which have further been used to evaluate corresponding transfer parameters Delta B-tr and Delta(tr)Delta H-dil(o), respectively. Positive DtrB values and negative Delta(tr)Delta H-dil(o) values indicate the predominance of hydrophilic-ionic interactions in these systems. Temperature dependence of B-coefficient and Delta H-dil(o) has also been discussed. Spectroscopic studies have been carried out to further investigate the structural changes and the interactions involved in the mixed aqueous solutions. (C) 2015 Elsevier Ltd. All rights reserved.