Single crystals of 1,2-o-isopropylidene-3,5-o-phenoxyphosphoryl--D-xylofuranose have been X-irradiated at low temperature (ca. 77 K) and studied by e.s.r. spectroscopy. The angular dependence of the signals has led to the identification of four radicals: a phosphoranyl-type radical, two phosphonyl species and a radical pair, one of whose components is a phosphonyl-type radical. The 31P-hyperfine tensor has been obtained for each species and the pair has been characterized by its electron–electron dipolar interaction. It is shown that electron capture by a PO bond and homolytic scission of the various P—O bonds are involved in the radiation damage process.