The effect of the preparation technique on the sorption-diffusion parameters of poly(3-hydroxybutyrate) (PHB) films was studied. The films formed by a single-stage technique have an axial texture of the crystalline phase, with the polymer chain oriented predominantly perpendicularly to the film plane. Moreover, the crystallites in PHB are preferably ordered in stacks in the course of diffusion; the alignment of the crystallites noticeably decreases the "sites" of PHB (polar groups) which are accessible to water molecules. As a result, the sorption capacity decreases but the rate of diffusion increases. On the contrary, PHB films prepared by a two-stage technique are characterized by a poor ordering of crystallites without texture organization. Here, the sorption/immobilization on the polar groups of PHB is increased, but diffusivities are decreased. Concentration dependencies of the water-diffusion coefficient are discussed. Additional information on the existence of protein impurities in the PHB samples obtained by the above two preparation techniques was obtained by FTIR spectroscopy and H-D exchange methods. (C) 2000 John Wiley & Sons, Inc.