The synthesis of 2,3-disubstituted poly(beta -peptide)s (nylon-3 analogues) bearing the benzyloxy group at position 3 and the diethoxymethyl or the isobutoxycarbonyl group at position 2, is described. Both optically pure and racemic forms were prepared for each case and all them were characterized by standard methods. The structure of these poly(beta -peptide)s was preliminary examined by X-ray diffraction and infrared spectroscopy. It was concluded that they do not tend to adopt the alpha -helixlike conformation characteristic of poly(beta -L-aspartate)s but rather a contracted conformation with amide groups in the nonassociated state.