The radiotherapy treatment of human cancer is often limited by the side effects and complications induced in normal surrounding tissues. The use of therapeutic strategies that could protect normal tissues while permitting the death of malignant neoplasm would be advantageous. Some studies have suggested that the amino acid glutamine (GLN) can serve as a conditionally essential nutrient in patients in a catabolic condition. The objective of this study was to evaluate the possible radioprotection of GLN on the frequency of chromosomal aberrations, number of metaphases with chromosomal aberrations and mitotic index in bone marrow cells of Rattus norvegicus. In this in vivo test system, GLN was administered by gavage at concentrations of 300 and 600 mg/kg body weight, in acute treatments, 30 min or 24 h before exposure to 3 Gy of whole-body gamma radiation. The results obtained in these experiments showed that GLN did not alter significantly the frequency of chromosome aberrations induced by gamma radiation under the experimental conditions used in the present study.