BACKGROUND: In vitro investigation of radioprotective properties of novel nutraceutical Gonebazol (Biofarm, Belgrade) has displayed its remarkable potential to reduce chromosomal aberrations and micronuclei induced by x rays. The goal of this study was to evaluate its protective properties in vivo. For this purpose, a group of medical staff performing invasive radiological diagnostics, that was identified to carry dicentrics in their lymphocytes, was selected for further monitoring. They consumed this nutraceutical for 3 weeks, 2 x 10 g per day (2 x 2 teaspoons dissolved in a glass of water). METHODS: Hematological parameters, chromosomal aberrations and micronucleus frequency were examined at the beginning of monitoring, on day 10 and 21 of the treatment. RESULTS: In the course of three weeks the incidence of chromosomal aberrations and micronuclei was significantly reduced (50%-80%), absolute number of granulocytes was lowered whereas the number of monocytes significantly was enhanced. This study has revealed that nutraceutic posses immunomodulatory properties seen as an improving monocyte-macrophage activity, which inversely correlates with incidence of lymphocyte micronuclei (r=0.75, p<0.05). CONCLUSION: Observed finding could be of particular importance in reducing cumulative effects of ionizing radiation in radiosensitive tissues and in preventing adverse health effects. No side effects were evidenced. Mechanisms of its immunomodulatory effects should be further examined.