The changes in weight and quality of sugarbeet roots stored in 18 clamps, mostly in eastern England during the winters of 1992/93 to 1994/95, were studied on farms using best commercial practice. Storage usually started in early December, at about the last recommended date of harvesting, and continued until the end of the beet-processing campaign at the local sugar factory (usually in February). Random samples of beet, in open-weave nets, were either analysed at the outset or were buried in a predetermined pattern in the clamp for up to 84 days. Periodically, samples were removed from the clamps for analysis. Beet weight hardly changed but sugar was lost as a reduction in sugar concentration: this declined at c. 0·02% per day. The concentration of reducing sugars, which are important impurities, increased fourfold during storage. Most other beet quality parameters remained unchanged. Sugar and adjusted weight was lost at 0·143 and 0·187% per day respectively. This relationship was highly significant, but a relationship between sugar loss and accumulated thermal time (0·0188% per °C day) accounted for more of the variation (73%). Temperature changes within the clamps, and the differences between clamps in accumulated thermal time, were not predictable. Some clamp insulation materials appear to allow more heat to accumulate than is desirable.