Ethene was copolymerized with 1-hexene in the presence of heterogeneous MgCl2/TiCl4 and homogeneous Cp2ZrCl2 catalysts to study the effect of 1-hexene addition on the ethene polymerization system. With both catalyst systems, 1-hexene had a rate-increasing effect. Compared with homopolymerization, the ethene consumption was increased as much as 8-fold with MgCl2/TiCl4 and 2.5 fold with Cp2ZrCl2. With Cp2ZrCl2 catalyst rate enhancement was apparent only when the polyethene was insoluble in the reaction medium. At higher temperature, where the product was soluble, there was no rate enhancement but rather a rate decrease.