This is the first study of changes in protein glycosylation due to exposure of human subjects to ionizing radiation. Site specific glycosylation patterns of 7 major plasma proteins were analyzed; 171 glycoforms were identified; and the abundance of 99 of these was followed in the course of cancer radiotherapy in 10 individual patients. It was found that glycosylation of plasma proteins does change in response to partial body irradiation (∼60Gy), and the effects last during follow-up; the abundance of some glycoforms changed more than twofold. Both the degree of changes and their time-evolution showed large inter-individual variability.