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- To develop the cytogenetic tool to detect chromosome damages after high dose exposure with 60Co γ-rays, dose-response curves were measured for induction of prematurely condensed chromosomes (PCC) in peripheral lymphocytes. Blood was obtained from 10 different healthy donors, and given okadaic acid (OA) in cultured lymphocytes for 1h after radiation exposure. Cells were analyzed by the frequencies of OA-induced PCC rings because it is difficult to obtain mitotic chromosomes using a conventional chromosome aberration (CA) assay. PCC-rings were scored in cells exposed in the dose range of 0.2-16Gy. The frequency of the cells with PCC and the dose-response relationship for the yield of PCC rings were examined in the irradiated lymphocytes.The yield of PCC-rings was increased up to 16Gy with dose dependent-manner. The observed dose-effect relationship for the percentage of cells with PCC-rings was calculated by linear-quadratic model. This technique can be applied to biological dosimetry of radiation exposures involving whole body irradiation to allow damaged chromosomes to be detected with great sensitivity.Detection of okadaic acid-induced PCC rings is a useful method up to 16Gy or more doses in estimating the absorbed doses of victims after high dose exposure. Calibration curves described in this paper will be used in our laboratory for biological dosimetry by PCC-ring after a high dose exposure.