Disclosed herein are biomarkers for determining gamma radiation exposure by an animal or human. The biomarkers include 3-hydroxy-2-methylbenzoic acid 3-O-sulfate, N-hexanoylglycine, .beta.-thymidine, taurine, xanthine, xanthosine, 2'-deoxyuridine, 2'-deoxycytidine, 2'-deoxyxanthosine, or any salt, ion, or combination thereof. Also disclosed are methods for determining gamma radiation exposure by an animal or human, which include the step of measuring the amount of one or more biomarkers specific to gamma radiation in the biological fluid and correlating the amount of said biomarkers to the amount of gamma radiation exposure by the animal or human. Systems for determining gamma radiation exposure by an animal or human and methods of treating an animal or human for gamma radiation exposure are also disclosed.