Densities of aqueous solutions of 16 organic electrolytes and polar solutes containing different functional groups al molality m approximate to 0.12 mol . kg(-1) have been measured at temperatures T = (298.15, 373.15, 448.15, and 523.15) K and at pressure p = 28 MPa. Densities of three of the solutions were also determined at T = 598.15 K. Partial molar volumes at infinite dilution V-2(infinity) and p = 28 MPa were calculated for each of the solutes at the various temperatures and the results used to evaluate group contributions to V-2(infinity) of the functional groups : CH3-, -CH2-, -CONH2, -COOH, -OH, and -NH2. The V(2)(infinity)s for most of the nonelectrolytes appear to be diverging in a positive direction at the higher temperatures, while V-2(infinity) for the electrolytes diverges in a negative direction. Temperature dependencies of V-2(infinity) for the solutes were analyzed in terms of four different semi-empirical equations employing temperature and temperature-dependent properties of water as variables. Parameters for each solute for the four equations are tabulated along with the standard deviations of the fits. All four equations reproduce the results reasonably well within the range of the measurements, but diverge widely above the temperature limits of the measurements. Two of the four equations have been fitted to the group volumes. These equations, along with the group additivity principle, were used to reproduce V-2(infinity) of the original electrolytes over the entire range of temperatures, showing that the group additivity principle is useful to at least T = 523 K. This suggests that these equations may be used to give reasonable estimates of V-2(infinity) from T = 298.15 K to T = 523 K for any aqueous organic solute which can be constructed from the six functional groups for which V(2)(infinity)s now exist.