Nascent polyethylenes of the high density and linear low density types prepared by gas phase polymerization, together with a series of nascent high density polyethylenes prepared by the slurry process, have been examined by X-ray diffraction, inelastic neutron scattering and Raman spectroscopy. The X-ray diffraction data and inelastic neutron scattering spectra show that the degree of crystallinity is smaller in the nascent samples than is commonly found in melt-crystallized materials. Low frequency Raman spectroscopy shows that the lamellar thickness is also smaller than usual. Melting and resolidification of the nascent, gas phase polymerized polyethylenes result in materials that more closely resemble the melt-crystallized products. The implications of the results are discussed as regards the crystallization process.