The dibutylmagnesium (Bu(2)Mg)-initiated polymerizations of L-lactide at 120 degrees C in bulk yielded poly(L-lactide) of low molecular weights (eta(inh) less than or equal to 0.4dlg(-1) in CH2Cl2), regardless of reaction time and initiator concentration. Higher molecular weights were obtained in solution when carried out in the presence of ethers. The addition of crown ethers to polymerizations conducted in toluene at 0 degrees C gave the best results, with eta(inh) values up to 3.0dig(-1) (in CH2Cl2), corresponding to number-average molecular weights (M(n)s) of the order of 3 x 10(5) g mol(-1). These high-molecular-weight poly(L-lactide)s possess almost complete optical purity and show melting temperatures of similar to 170 degrees C. Relatively high-molecular-weight poly(D,L-lactide)s were also obtained by the Bu(2)Mg-initiated polymerizations of racemic- or meso-D,D-lactides, with eta(inh) values up to 1.4 dig(-1) (in CH2Cl2), corresponding to M(n) = 10(5), being found. The Grignard reagent, BuMgCl, gave somewhat better results than Bu(2)Mg when used as an initiator for L-lactide in bulk. However, BuMgCl is not reactive enough to initiate satisfactory polymerizations in solution at temperatures less than or equal to 25 degrees C.