Acoustic velocities have been measured within a 38 cm cubic block of granite isolated from the surrounding rock. The block was subjected to uniaxial stresses in the range 0--24 MPa and to heating in the range 14¿ to 98 ¿C. An increase in temperature from 14¿ to 72 ¿C in the unstressed block resulted in an increase in velocities in directions parallel and perpendicular to the applied stress. A further increase in temperature to 98 ¿C in the unstressed block resulted in a decrease in velocities. Application of uniaxial stress with the block at a temperature of 98 ¿C resulted first in uniform increases in velocity to an applied stress of MPa and then sharp decreases from 10 to 14 MPa, followed by uniform increases in velocity to a maximum stress of 24 MPa. A reduction in temperature to 16 ¿C resulted in a sharp reduction in velocity, 25 percent less than originally measured at ambient temperature. It is concluded that, at temperatures rising to 72 ¿C, anisotropic thermal expansion of the crystals comprising the granite causes the closure of microcracks present in the unheated rock. Between 72¿ and 98 ¿C, particularly when stress was applied, irreversible mechanical changes occurred in the block.