Equipment has been constructed for experimentation at very high pressures and temperatures. With the modified Bridgman anvil device described, it has proven possible to maintain pressures in excess of 100 000 atm simultaneously with temperatures above 3000°C for periods greater than one hour. [The fixed points used to infer this pressure are taken to be the pressure values established by Bridgman for discontinuities of the electrical resistance of bismuth and barium, 25 650 kg cm−2and 80 000 kg cm−2, respectively, and called the bismuth and barium points. Recent unpublished work indicates that the barium point pressure will probably have to be revised downward materially, reducing our pressure estimates in the upper range.] The use of an extrudable plastic compressible gasket is described. Several considerations are presented concerning the support of high pressure components constructed of cemented tungsten carbide. Coesite, almandite, and diamond have been synthesized in the apparatus.