Abstract: An olefin polymerization process in which at least two introductions of hydrogen are made during the olefin polymerization reaction. Suitable catalysts include metallocenes of the general formula (Cp).sub.m TiX.sub.n, wherein Cp is a substituted or unsubstituted cyclopentadienyl ring, X is a halogen, m=1-2, n=2-3, and wherein m+n=4, and conventional Ziegler-Natta catalysts blended with or modified by such metallocenes.