The initial rates of ethylene polymerization initiated by 13 chelating tertiary diamine:n-butyllithium complexes were determined under a standard set of conditions. Complexes of the cyclic diamines 1,2-dipyrrolidinoethane, sparteine, and 1,2-dipiperidinoethane resulted in higher polymerization rates and larger ultimate polymer yields than did complexes of acyclic diamines such as N,N,N′,N′-tetramethylethylenediamine. The rates of polymerization and also the polymer yields were also strongly affected by the length of the chain segment connecting the two amino groups in the diamine. Two carbon segments were superior to three carbon segments which were better than one or four carbon segments. The decomposition rate of n-butyllithium was also strongly accelerated by the presence of many of these diamines.