Thermal stability of neutral Zn(II), Pd(II) and Pt(II) complexes of formulae [Zn(apsox)(2)](.)3H(2)O and [M(apsox)Cl] (M=Pd(II), Pt(II), HL=(E)-2-oxo-2-{N -[1-(pyridin-2yl)ethylidene]hydrazino)acetamide) were studied. The results of DSC and TG analyses within the temperature range from 20 to 600 degrees C in nitrogen atmosphere showed that the loss of crystal water represents the first step during decomposition of the octahedral Zn(II) complex followed by structural rearrangement of its anhydrous form. After that the complex remained stable to about 330 degrees C. Different from neutral square-planar Pd(II) and Pt(II) complexes, a satisfactory resolution of the peaks in DSC of the Zn(II) complex enabled determination of the activation energies of its structural transformation and thermal degradation.