The potential use of flavonoids as a radioprotector is of increasing interest because of their high antioxidant activity and abundance in the diet. The aim of this study is to examine genotoxic and radioprotective effects of one of the most common flavonoids, apigenin, on radiation-induced chromosome aberrations in human lymphocytes. The cytokinesis-block micronucleus (CBMN) assay was used to evaluate such effects of apigenin. Blood samples were collected from two non-smoking healthy male volunteers who had no history of previous exposure to other clastogenic agents. Isolated lymphocytes were cultured. There were two tubes per concentration for all treatments. To evaluate the genotoxicity of apigenin, cells were first treated with different concentrations of apigenin (0, 2.5, 5, 10 and 25 microg/mL) at 24 h after culture initiation, followed by cytochalasin-B (Cyt-B) treatment (3 microg/mL) and cell harvest at 44 and 72 h, respectively. Secondly, to investigate the radioprotective effect, cell cultures were exposed to different concentrations of apigenin as described above for 30 min before being irradiated to 2 Gy of 137Cs gamma rays (at a dose rate of 0.75 Gy/min). In all instances, the frequency of MN was scored in binucleated (BN) cells. The nuclear proliferation index also was calculated. We did not detect an increase in the frequency of MN in non-irradiated human lymphocyte cultures treated with 2.5, 5.0 or 10 microg/mL apigenin; although, we did observe an increase in cultures treated with 25 microg/mL apigenin (the highest concentration of apigenin used in our study). We also observed a significant increase in the frequency of MN in irradiated cells overall; however, the frequency was decreased as the concentration of apigenin increased, suggesting a radioprotective effect. These findings provide a basis for additional studies to help clarify the potential use and benefit of apigenin as a radioprotector.