In this work, the catalytic degradation of high and low density polyethylenes, using catalysts based on transition metals supported on zeolite Y, is analysed using simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The results obtained in the catalytic degradation are compared with those that were obtained in the purely thermal degradation. The transition metals used, vanadium, zirconium and nickel, supported on NaY or HY were studied since they were found to be active, although with different degrees of efficiency, for ethylene polymerization, which is, in a way, the reverse reaction of the one we are interested in. it was found that they are also able to promote the degradation process of polyethylene, also with varying efficiencies. A kinetic model capable to describe the performance of the catalytic degradation, and which has already been used to analyse its thermal degradation, has been applied. Fitting this model to the experimental results obtained by TG and DSC made it possible to estimate several kinetic parameters and to gain some insight into the processes involved. (c) 2009 Elsevier B.V. All rights reserved.