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- The goal of this study was to provide data on the dose-dependent production of micronucleus (MN) in human lymphocytes irradiated with 60Co γ-rays and 50MeV neutron, and to evaluate predictive markers of intrinsic radiosensitivity in individuals for monitoring occupational or environmental radiation exposure.For the dose-response study, heparinized whole blood of 10 healthy volunteers was irradiated with 60Co γ-rays employing of 0.25-8Gy. The MNs were observed all doses, and the numerical changes according to doses. In dose-response curves fit linear-quadratic form (alpha =0.31±0.049, beta =0.0022±0.0022) for γ-rays, but (alpha =0.99±0.528, beta =0.0093±0.0047) for neutron. Neutrons were than γ-rays effective in producing MN with dose-dependent manner. The frequency of MN varies with dose. The RBE (relative biological effectiveness) for micronuclei was 2.370.17.Further studies were carried out to provide evidence for the existence of individual variations in age-dependent responses to radiation. Spontaneous and radiation-induced MN varies greatly among individuals, and little is known about the molecular mechanisms of this variability. It was shown that the increased level of spontaneous cell with MN was observed with increasing age. The relationship between radiosensitivity and the increased spontaneous level of MN may be in inverse proportion.These studies indicates that the MN assay have a high potential as a rapid, sensitive and accurate method which can be used to monitor a large population exposed to radiation for rapid triage in the case of a large-scale accident.