Pyrolysis of certain polyammoniates of boron hydrides of metals (PABH Mes) at high pressures not exceeding 7.0 GPa and at a temperature not exceeding 1770 K was examined. These compounds have a general formula Me(BH 4 ) n · m NH 3 , where n is determined by the metal valency, m =1–8, Me: Li, Mg, Zn, Al, Sc, La, Zr, Cr, Co. P,T regions of cubic boron nitride (cBN) synthesis in the process of PABH Me pyrolysis were determined. It was ascertained that the P,T regions differed widely for different compounds. The kinetics of cBN formation in the process of pyrolysis of PABH Mg and PABH Al were studied. Cubic boron nitride crystals were examined using the method of scanning electron microscopy (SEM). A mechanism of cubic boron nitride formation in the process of PABH Me pyrolysis is suggested.