A kinetic study of the ethylene-styrene copolymerization in the presence of rac-(ethylenebis(1-indenyl)zirconium dichloride activated by MAO shows the peculiar behavior of this catalytic system that is known to produce crystalline nearly alternating copolymers. Some inferences on the monomer-metal interactions are made on the basis of this study. The parallel investigation on the catalyst based on isopropylidene(l-cyclopentadienyl)(9-fluorenyl)zirconium dichloride allows us to produce a stereoregular nearly alternating ethylene-styrene copolymer also with this catalytic system. The same main tacticity seems to characterize the copolymers obtained with the C-2 and C-s symmetric catalysts in accordance with the generally accepted mechanism of stereocontrol in the l-alkene polymerizations.