The reactivity of PbF4 with ammonia and NH4F wag investigated by in situ experiments like thermal analysis as well as time- and temperature resolved X-ray diffraction. The thermal decomposition reaction of PbF4 under nitrogen was recorded. In a second experiment the solid state reaction of PbF4 with NH4F was performed under an atmosphere of ammonia and led to (NH4)(3)PbF7. The structure of (NH4)(3)PbF7 was solved isostructural to (NH4)(3)SnF7 in space group Pm3m with the lattice constant a = 613.82(1) pm. In this structure two kinds of PbF62- anions are present with one kind exhibiting rotational disorder.