The polyethylene obtained in the presence of the catalyst constituted by the meso isomer of the prototypical zirconocene complex (ethylene)bis(l-indenyl)zirconium dichloride activated by methylalumoxane is characterized by the presence of ethyl branches. The intensities of the C-13 NMR signals associated with these branches indicate that there are about 1-2 ethyl groups per 100 monomer units. As a consequence, the melting temperature is 10-15 degrees C lower than the linear polyethylene obtained with the rac mixture of the same zirconocene complex. On the basis of kinetic evidence, a branching mechanism that involves a beta-H transfer to the coordinated ethylene is proposed.