H-1 and P-31 NMR techniques were applied to study the changes in metabolite profiles in human urine resulting from radiation exposure following the Chernobyl reactor accident. In cases of acute leukemia and different accumulated doses of external radiation (from 0.20 to 4.00 Sv), the proton spectra were classified on the basis of the peaks due to N-trimethyl groups, creatinine, citrate, glycine, and hippurate. Unidentified resonances were observed between 15.9 and 21.4 ppm in six phosphorus spectra of patients with preleukemia and acute leukemia. Characteristic spectral changes were similar for external radiation and incorporation-induced internal irradiation. The spectral patterns described may serve as a criterion of radiation injury.