Density measurements were carried out on dilute solutions of tetramethylurea (TMU) in normal and heavy water in the aquamolality ranges 0.058-1.74 and 0.052-1.72, respectively, at 278.15 K, 288.15K. 298.15K. 308.15K, and 318.15K. The excess partial molar volumes of TMU ((V) over bar (E,infinity)) and volume second virial coefficient (nu(xx)), calculated from the densities of the HID isotopically distinguishable solutions, are negative, which indicate that the solute has a predominantly structure-making effect on aqueous surroundings. With decreasing temperature and on going from protiated solvent to deuterated one the values of (V) over bar (E,infinity) and nu(xx) become more negative, suggesting that the hydration sphere around a TMU molecule is more structured in the specified cases. The obtained results were discussed allowing for enthalpic and some other characteristics of TMU solutions in normal and heavy water. (C) 2009 Elsevier B.V. All rights reserved.