An alcoholysis method is described for the modification of high molecular weight poly(p-benzyl L-asparatate) ; by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n-propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L-aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(gmethy1 L-aspartate) has the left-handed helix sense, the others are right-handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising t,he temperature of chloroform solutions of the right-handed form of the copolymers of benzyl L-aspartate and ethyl L-aspartate results in a transition to the left-handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(@-npropyl L-aspartate) undergoes a transition from the right-to the left-handed helix form a t 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right-or lefi-handed helical form.