The catalytic activities of two metallocene compounds, EtInd(2)ZrCl(2) and Ind(2)ZrCl(2), in the polymerization of ethylene depend heavily on certain parameters, such as Zr concentration in the reaction, type of the reactor, and stirring speed for homogeneous catalysts. One way or another, all these factors influence the catalytic activity of these systems, but catalyst concentration and stirring speed are the most important ones. In the case of heterogeneous catalysts of the same metallocenes, the most pronounced influence is related to the type of support and its porous nature. The influence of the support on activity and morphology is shown.