Background: Most of the cytogenetic dosimetry, except Premature Chromosome Condensation assay, saturates at 6 Gy. Present studies are aimed to assess feasibility of simple CB-MN assay for prescreening of high dose accidental exposures. Materials and Methods: Human peripheral blood lymphocytes from two donors were gamma irradiated to different doses ranging from 0-15Gy, cultured for 72 h. Cytochalasin-B was added to the cultures at 44 h. Slides were analyzed for frequency of Mononucleated cells (MNC), ratio of Tri/Quadra nucleated cells, micronuclei ( MN ) yield in MN positive cells, mitotic bridges and apoptosis. Results: At 5 Gy 67% Mononucleated cells, 0.22% apoptotic cells and 1.76% mitotic bridges were observed. Micronuclei yield in MN positive binucleated cells was found to be 1.43±0.04. At 8Gy 96.63% Mononucleated cells, 22.64% apoptotic cells and 3.8% mitotic bridges were observed. Micronuclei yield in MN positive binucleated cells was found to be 2.18±0.18. At 15 Gy, 99.6% of the cells were Mononucleated and 0.38% was binucleated and MN yield was 2.9 ±0. The total number of MN in MN positive cells increases with increasing radiation doses. Conclusion: All the three indicators number of MN in all binucleated cells (BNC) , number of MN /MN positive binucleated cells and the nuclear division index (NDI) can serve as good biomarkers for biodosimetry at high doses. Although the frequency of mitotic bridges and apoptotic bodies increases with dose, there is no consistent difference between various doses. Thus the CBMN + NDI assay can be a biodosimetry method at high doses.