The isothermal and non-isothermal transformations of polycrystalline CuNH4PO4. H2O in vacuum and in various gas atmospheres (in open air and in gaseous ammonia atmosphere) were studied at 20-800 degrees C by means of differential thermal analysis, thermogravimetry, X-ray diffraction, paper chromatography, optical microscopy and chemical analyses. The effects of the gas phase composition on the kinetic peculiarities of total gas evolution and on the partial processes of dehydration, ammonia removal and rearrangement of the anionic sub-lattice were considered.