By analogy to the techniques applied for monitoring biological effects of exposure to genotoxic agents in occupational populations, we have carried out cytogenetic monitoring in a group of inhabitants of a village (Mellery, Belgium) suspected to have been exposed to a variety of toxic environmental pollutants. These pollutants probably originated from a neighboring chemical wastes site. A group of 51 environmentally exposed and 52 reference persons (including children) were examined for the frequency of sister-chromatid exchanges (SCE) in their peripheral blood lymphocytes. The technique was further refined by using a high frequency cells (HFC) analysis. Analysis of the reference subgroups showed a significant difference between non-smoking adults and children. The influence of tobacco was clear, too. In the exposed group, no significant differences could be demonstrated between either the smokers or the non-smokers or the children. Furthermore, not only were the mean frequencies of SCE higher than in the respective reference subgroups but comparison between the two groups also showed a higher number of individuals presenting a HFC level above the background in the exposed group. Surprisingly, the difference was more pronounced for the children. A follow-up of the same exposed population carried out 18 months later and after remediation of the atmospheric chemical release, the previously observed tendencies in the exposure parameter remained unmodified.