The apparent molar volumes, V-2,V-phi, apparent molar adiabatic compressibilities, K-S,K-2,K-phi, and heats of dilution q of glycyl-glycine (gly-gly), glycyl-glycyl-glycine (gly-gly-gly), glycyl leucine (gly-leu), and glycyl-glycylleucine (gly-gly-leu) have been determined in aqueous trimethylamine N-oxide (TMAO) at T = 298.15 K. These data have been used to calculate the values of infinite dilution standard partial molar volume V-2,V-m degrees, standard partial molar isentropic compressibility K-S,K-2,K-m degrees, standard molar enthalpy of dilution Delta H-dil degrees, and the corresponding transfer thermodynamic properties from water to aqueous TMAO solutions. The results on transfer thermodynamic properties of peptides from water to aqueous TMAO solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic, hydrophilic-hydrophobic, and hydrophobic-hydrophobic group interactions. The results obtained in this work suggest strengthening of polar solute-solvent interactions in case of peptides compared to those in case of amino acids and support the experimental observations on the effect of TMAO on the thermodynamic and conformational stability of proteins. (C) 2012 Elsevier Ltd. All rights reserved.