Upon contact with ethylene, the Phillips Cr/silica catalyst must self-alkylate before polymerization can begin. How this happens has been a mystery for over 60 years, being not only of scientific interest but also of commercial importance. Consequently, many controversial schemes have been proposed, including some that hold the initial PE chain to be different from all subsequent chains, starting with a vinyl group, instead of the usual methyl group. In this study, polymer chains produced by the Cr(II)/silica-titania catalyst at low yield were analyzed in an effort to identify the starting group on the first chain produced. The PE/Cr yield was deliberately kept low to avoid diluting that initial chain with other chains produced afterward. The polymer was then characterized by gel permeation chromatography and C-13 NMR (natural abundance). Strong signals from methyl end groups were present, but terminal vinyl groups were not detected. Likewise, analysis by proton (H-1) NMR also indicated a general lack of vinyl chain ends. An attempt was also made to identify the first species on the initial chain through isotopic labeling. Deutero-ethylene (C2D4), deutero-propylene (C3D6), or C-13-ethylene was first "preadsorbed" onto the divalent catalyst at -78 degrees C, where polymerization does not occur. After evacuating the excess isotopically labeled monomer, polymerization was conducted with unlabeled ethylene (C2H4) at higher temperatures. Deuterium (H-2) NMR analysis of the polymers again indicated a strong methyl signal but no resonance from deuterium-containing vinyl chain ends. Comparison of the different NMR methods indicated a high degree of deuterium enrichment in the methyl chain ends. These results indicate that the initial chain in these experiments began with a methyl group, not a vinyl group as has sometimes been contemplated. Although helpful, this information still leaves the mechanism of site alkylation unclear because there is not enough hydrogen in ethylene to produce a methyl-initiated chain, ,without some other (still undefined) reaction also being involved to furnish the additional hydrogen, such as the creation of a permanent ligand.