The kinetic data on ethylene polymerization over homogeneous catalysts based on -1,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) and cobalt(II) chlorides (LMCl2, M = Fe, Cc) with different aluminium-organic activators (MAO, AlMe3, Al(i-BU)(3)) are reported. LFeCl2 is very effective with AlMe3 and Al(i-Bu)(3) as activator and LCoCl2 is highly active in the presence of AlMe3. For MAO as activator, the activity depends on the content of free AlMe3 in MAO. Maximal activity has been found for MAO completely purified from free AlMe3. According to H-1 and H-2 NMR study, formation of the similar neutral intermediates of the type [LFe(II)Me(mu-Me)(2)AlMe2] have been detected for LFeCl2/AlMe3 and LFeCl2/MAO catalysts. In the system LCoCl2/MAO, the complex of the type LCo(II)Me(X).MAO (X = Me or CI) with terminal Co-Me group is detected. Interaction of LCoCl2 with AlMe3 results in the formation of diamagnetic Co(I) species. Highly active supported catalysts SiO2/LFeCl2 + AIR(3) and SiO2/MAO/LFeCl2 have been prepared. In contrast to homogeneous systems, the supported catalysts are stable at elevated temperatures of polymerization (70 degreesC) and produce high molecular mass polyethylene with improved morphology. (C) 2002 Elsevier Science B.V All rights reserved.