Single crystals of L-O-serine phosphate, (HOOC)CH(NH3+)CH2OPO3-H, were X-irradiated at 295 K and studied using EPR, ENDOR, and FSE techniques. At this temperature, three carbon-centered radicals were identified. Radical I, the deamination product (HOOC)CHCH2OPO3-H, is shown to have undergone a major molecular reorientation upon formation. Radical II is identified to be the product (HOOC)CH(NH3+)CHOPO3-H. This species exhibits a nonplanar site for the lone electron density. This deviation from planarity is ascribed to electrostatic interaction between the lone electron orbital and lone pairs centered on the neighboring oxygen atom. Hyperfine interaction with the beta-nitrogen of the amino group is observed. Both the N-14 hyperfine and quadrupole coupling tensors are determined and the signs of the hyperfine coupling tensor principal values are deduced from interpretation of the quadrupole tensor employing the Townes-Dailey approach. The beta(14)N isotropic interaction is well described by a Heller and McConnell type cos(2) theta rule. The results found in the present work, together with other recent observations, yield estimated values of the constants B-0 = 1.0 MHz and B-2 = 34.5 MHz. Radical III exhibits the structure (HOOC)CH(NH3+)CH2, formed by scission of the phosphate-ester bond at the carbon side. No beta(14)N coupling is observed fur this radical due to a dihedral angle close to 90 degrees. Possible mechanistic routes for the formation of these radicals are discussed in comparison with previously published data on serine and other alkyl phosphate derivatives.