This project utilizes state-of-the-art molecular cytogenetic techniques to determine the frequency of stable cytogenetic damage in peripheral T lymphocytes of people involved with the Chernobyl nuclear reactor accident. The first study group is "liquidators," i.e. people who helped clean up the radioactivity in and near the site of the damaged reactor. A second group consists of matched controls (people of similar age, smoking status, and lifestyle) who did not participate in the clean-up activities. Fluorescence in situ hybridization with chromosome-specific composite DNA probes ("chromosome painting") will be used to measure the frequency of stable chromosome aberrations, i.e. translocations and insertions, in these groups of people. The purpose is to improve our understanding of the long-term cytogenetic consequences of low-dose radiation effects in people. Our goals are to: (1) improve our preliminary characterization of the radiation doses received by the liquidators; (2) conduct a detailed statistical analysis of the questionnaire data to determine which, if any, lifestyle factors influence translocation frequencies in exposed and control subjects; (3) analyze aberrant cells from selected donors to determine the extent and hence the importance of clonal expansion for biodosimetry by cytogenetics; (4) provide biological dose estimates to evaluate the relative magnitude of response of the results of the GPA and HPRT projects; and (5) determine how the cytogenetics data can be combined with the GPA and HPRT data to improve the detection and characterization of low-dose radiation exposure in humans. We will also determine how these combined endpoints and contribute to improving our understanding of the mechanisms and health consequences of radiation-induced genetic damage. In conjunction with the GPA, HPRT and statistical efforts of this Program Project, this work will lead to a greatly increased understanding of the long-term effects of human exposure to ionizing radiation.