Development of radiation technology has resulted in increasing numbers of people working with it. Therefore it has increasingly been important to monitor the radiation in order to ensure public safety. Physical dosimetry plays an important role in monitoring. But a need arise for biological dosimetry where physical dosimetry is absent or its presence is insufficient. In this study Co-60 gamma radiation dose-response curves for chromosome aberrations were determined for use as controls in biological dosimetry. Peripheral blood that were taken from healthy individuals not working with radiation were irradiated at different radiation doses. The relationship between unstable chromosome aberrations in metaphaseblocked cells and radiation dose were drawn by using the linear-quadratic (LQ) formula. The absorbed radiation doses of the test group consisting of five people that had been working with Co-60 teletherapy machines were estimated using the LQ parameters of control dose-response curves in the Qdr method. Estimated radiation doses were below the permissible radiation dose-limits for four workers, but one worker's estimated dose was higher than these limits.