The kinetics of chain degradation of purified granules of poly(beta-hydroxybutyrate) in 3.0 N HCl at the boil were followed using gel permeation chromatography to detect changes in molecular weight of the residue. The results showed that degradation corresponded to a model of random scission of the molecules of both the crystalline shell and the non-crystalline core indiscriminately. Differential scanning calorimetry and wide-angle X-ray diffraction results demonstrated that the molecules recrystallize due to chain scission and annealing at the temperature at which degradation is performed (104.5 degrees C). Transmission electron microscopy of enzyme-isolated, spray-dried granules revealed a retention of the surface shell throughout the reaction with conversion of the core to a porous lamellar texture.