Forty-eight individuals, who received protracted low-dose rate gamma-irradiation from radioactive environments for 2-10 years, have been evaluated repetitively for cytogenetic damage by the cytochalasin-B micronuclei assay (CBMN) after they relocated from radioactive buildings. These subjects were shown to have a significant decrease in the CBMN frequencies during 26.2+/-8.4 months of follow-up. By the mixed effect multiple linear regression analysis, the CBMN frequencies in these 48 subjects during repetitive measurements were significantly associated with the relocation duration since leaving the radioactive environments (relocation time or RT in months; estimate -0.47, standard error 0. 0016, p value 0.0074). The alteration rate in the proportions of binucleates carrying a single micronucleus and those with multiple micronuclei was further compared among 26 of these exposed individuals. The proportions of binucleates with multi-micronuclei were shown to decline significantly faster than those with a mono-micronucleus between these two repetitive assays (proportional Z-test, p value 0.003). Moreover, some of the exposed subjects were shown to have a persistent increase in the total micronuclei frequencies or carrying multi-micronuclei in the binuclei even 3-4 years post-cessation of exposure. This suggests potential genomic instability in stem cells of the exposed individuals and the phenomenon deserves further closer monitoring. Understanding the dynamics of micronucleus expression in lymphocytes in subjects with previous mutagenic exposure would be of significant importance for human population monitoring.