Polymerization of ethylene catalyzed by a blend of INPETUS(R), a Ziegler-Natta catalyst, with some half metallocenes such as CpTiCl3 (1), CpMCl3 (M = Ti, Hf) (2,3) and IndZrCl(3) (4) or with tris(pyrazolyl)borate complexes like TpTiCl(3) (5) and Tp*TiCl3 (6) in the presence of MAO, was carried out in a single reactor. Activities of the mixtures using the half metallocenes (2) and (3) were higher than those obtained with (1) and (4). On the other hand, the blends with tris(pyrazolyl)borate complexes (5) and (6) showed the lowest activities of both types of complexes used. Molecular weight of polyethylene (PE) obtained from the mixture with CpTiCl3 (2) was slightly higher than that of PE obtained with INPETUS(R) and the complex (6) and higher than those of the blends studied in this work. Molecular weight distribution (MWD) of the PE from INPETUS(R)/IndZrCl(3) (4), produced at very mild reaction conditions, was considerably similar to a type of PE obtained in industrial plants under more severe reaction conditions. The polymers resulting from these blends showed melting temperatures characteristic of HDPE. (C) 2002 Elsevier Science B.V. All rights reserved.