Hot-pressing techniques have been developed for a 2000-ton uniaxial split-sphere apparatus (USSA 2000) to fabricate polycrystalline specimens of high-pressure phases of mantle minerals at pressures up to 18 GPa and temperatures up to 1400¿C. Cylindrical specimens (3 mm in diameter and 2--3 mm long) of the beta-phase of Mg2SiO4 were synthesized using a NaCl cell and recovered at ambient conditions by simultaneously decompressing and cooling along a computer-controlled P-T path designed to preserve the high-pressure phase and anneal strains in the polycrystalline aggregates. These specimens are single-phased, fine-grained (≤5 micron), free of microcracks and preferred orientation and have bulk densities greater than 99% of x-ray density. Ultrasonic interferometry measurements of the P-wave and S-wave velocities demonstrate that the polycrystals are isotropic and exhibit velocities within 2% of the Hashin--Shtrikman averages calculated from the single-crystal elastic moduli. The successful fabrication of these high-quality polycrystalline specimens makes feasible experiments to determine the pressure dependence of the acoustic velocities for high- pressure phases of mantle minerals. ¿ American Geophysical Union 1990