The kinetics of the anionic polymerization of methyl methacrylate using THF as solvent, 1,1-diphenylhexyllithium as initiator and sparteine as ligand has been investigated in a flow-tube reactor for initiator concentrations higher than 1 x 10(-3) mol l(-1) and a temperature range between - 10 and 20 degreesC. Addition of sparteine induced a decrease in both the reactivity of the growing enolates and the extent of termination reactions. While a fractional kinetic order relative to the active centres was obtained in the presence of sparteine, this additive shifted the equilibrium between aggregated and unimeric species toward the formation of unimeric-ligated enolates as indicated by entropic and enthalpic parameters of the aggregation equilibrium. The rate constants of propagation and termination of these growing species were also determined.