alpha,beta-Poly(N-hydroxyethyl)-DL-aspartamide (PHEA) and alpha,beta-polyasparthydrazide (PAHy) are synthetic polymers previously studied for biomedical applications. We report here the results of a small-angle X-ray scattering analysis carried out on these two macromolecules in aqueous solution. The data obtained indicate that the two polymers assume remarkably different conformations in aqueous solution, although the backbone is supposed to be the same for the two chains. PHEA can be represented by a random coil conformation, whereas PAHy can be described in terms of an elliptical cylinder characterized by an almost planar structural arrangement with the backbone refolded on itself in a fashion somewhat similar to the beta layer of globular proteins. This more rigid conformation of PAHy is related both to the network. of hydrogen bonds capable of stabilizing the overall structure and to the lower molecular weight with respect to PHEA. Conformational and energetic analyses of PAHy are also discussed.