In the present work a decrease of NDI was detected with increasing radiation doses; similar results were reported by Bolognesi et al.[2]. We also found a correlation between NDI and micronucleus formation in the data of the 16 donors (p < 0.01) and also in the age(p < 0.05) and gender (p < 0.01) sub-groups. Although the NDI is not sufficiently robust for direct application as a biological dosimeter, it can be employed to indicate alterations to the cell cycle that can be induced by exposure to ionizing radiation [6]. Furthermore, it has been reported that the NDI can be an useful tool in dose-estimation after accidental high-dose exposures (exceeding 5–7 Gy), in combination with the CBMN assay [41].All doses from the pooled data present u-values above 1.96, which indicates over-dispersion and hence deviation from a Poisson distribution. Several other studies also showed the same tendency for over-dispersion in micronucleus distribution [39,42,43]. Unlike the dicentrics, the distribution of micronuclei in irradiated cells commonly exhibits over-dispersion, since itis difficult to determine if the exposure is a total or a partial body irradiation.