Poly(aspartic acids) of different chain lengths (11, 14, 18, 24, 30, 52, 58, almost-equal-to 115) were prepared, for the use in aminoglycoside-induced nephrotoxicity inhibition studies, some in their pure L- or D-configuration and in pure alpha-linkage form by the polymerization of alpha-amino acid N-carboxyanhydride (NCA) derivatives with a variety of dialkyl aspartate molecules as primary amine initiators. The primary amine chosen served as an internal reference in the H-1 NMR spectrum for the estimation of the degree of polymerization (chain length) in these molecules. Poly(aspartic acids) with varying amounts Of D and L asymmetric centres and in pure alpha-linkage form were also prepared. Poly[(alpha-CO-beta)(L-CO-D) aspartic acid] was prepared by a simplified thermal polymerization procedure for biological studies and also to study the tacticity effects in its C-13 NMR spectrum. A qualitative correlation was demonstrated between the retention times from gel-permeation chromatographic analysis and the H-1 NMR method used to estimate the polymer chain length.