Using a synchrotron source, in. situ small-and wide-angle X-ray studies of the gelatinization of 40% potato starch slurries were carried out. By determining how the crystallinity index changes with temperature, it is possible to follow the destruction of the crystals. Fitting the (100) peak of the starch structure has shown that the crystals change only slightly in dimension over the temperature range studied. The large-scale swelling which occurs during gelatinization is associated with amorphous regions of the starch granule structure.