The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed aggregates of lithiated organic compounds support the complexity of these systems. Lithium diisopropylamide (LDA) shows the highest initiation efficiency (e.g., f = 75% in THF at -78 degrees C). Interestingly enough, lithium chloride has a remarkable beneficial effect on the methacrylates polymerization in THF at -78 degrees C, due to the formation of 1 : 1 mixed dimer with LDA, which promotes a well-controlled anionic polymerization (M-w/M-n = 1.05) with a high initiation efficiency (94%). The less bulky lithium-diethylamide (LDEA) is much less efficient (f = 26%), essentially as a result of some associated "dormant" species and side reactions on the carbonyl group of MMA. Although various types of ligands have been screened, no remarkable improvement of LDEA efficiency has been observed. Lithium bis(trimethylsilyl)amide (LTMSA) has also been used to increase the steric hindrance of the initiator. This compound is, however, unable to initiate the methacrylates polymerization, more likely because of a too low basicity and a too strong Li-N bond.