A thermodynamic method in which all physical properties (derivatives of the Helmhotz energy) are determined from seven thermoelastic parameters is used to calculate density isentropes of (Mg,Fe)SiO3 perovskite for lower mantle conditions. We find that, provided the EoS constants, &rgr;0, KT0, and K'0, are known, the density distribution can be found from the thermal pressure and often from the thermal pressure evaluated at zero pressure. Three isentropic density distributions of perovskite are calculated and are shown to be nonparallel with PREM's density distribution. This leads to the speculation that a lower mantle entirely composed of perovskite may not be phase homogeneous throughout its whole depth. ¿ American Geophysical Union 1995