4-Vinylcyclohexene (VCH) and cyclooctadiene (GOD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis(1-eta(5)-indenyl) zirconium dichloride (1) as a catalyst precursor. Homopolymerizations of VCH, vinylcyclohexane and cyclohexene were compared. The parameter K(pi)k(p), which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexane but is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and towers the polymer MW by about two-fold. COD has very low activity as a termonomer.