Nickel(II) and palladium(II) complexes with a-dioxime ligands dimethylglyoxime, diphenylglyoxime, and 1,2-cyclohexanedionedioxime represent six new precatalysts for the polymerization of norbornene that can be activated with methylaluminoxane (MAO), the organo-Lewis acid tris(pentafluorophenyl)borane [B(C6F5)(3)], and triethylaluminum (TEA) AlEt3. The palladium but not the nickel precatalysts could also be activated by B(C6F5)(3) alone, whereas two of the three nickel precatalysts but none of the palladium systems are somewhat active with only TEA as a cocatalyst. It was possible to achieve very high polymerization activities up to 3.2 (.) 10(7) g(polymer)/ mol(metal) (.) h. With the system B(C6F5)(3)/AlEt3, the activation process can be formulated as the following two-step reaction: (1) B(C6F5)(3) and TEA lead to an aryl/alkyl group exchange and result in the formation of Al(C6F5)(3)Et3-n and B(C6F5)(n)Et3-n; and (2) Al(C6F5)(n)Et3-n will then react with the precatalysts to form the active species for the polymerization of norbornene. Variation of the B:Al ratio shows that Al(C6F5)Et-2 is sufficient for high activation. Gel permeation chromatography indicated that it was possible to control the molar mass of poly(norbornene)s by TEA or 1-dodecene as chain-transfer agents; the molar mass can be varied in the number-average molecular weight range from 2 (.) 10(3) to 9 (.) 10(5) g (.) mol(-1).