Three types of hollow microspheres with different average diameters (100-150 mu m) and two aluminium alloys as matrix material were used to produce metal matrix syntactic foams (MMSFs) by pressure infiltration. The phases, which formed at matrix-filler interface, were investigated by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The investigation showed that in syntactic foams, with the Al99.5 matrix, an exchange reaction took place between the matrix and the amorphous components of ceramic hollow microspheres. The reaction resulted in significant formation of alumina and Si precipitates. Because of this diffusion reaction, the hollow microspheres' walls were degraded. In the case of the AlSi12 matrix the reaction was suppressed by the considerable Si content of the matrix. Therefore, the wall of the hollow microspheres remained unharmed and no real interface layer was found.