THERE are some correlations between cell's ability to remove DNA damage and proliferative activity. Another phenomenon was observed that the frequency of radiation-induced aberration can be influenced according to the concentrations of colcemid or colchicine which used for arresting the cell cycle in metaphase. The aim of this study is to improve the technical accuracy of the chromosome aberration analysis and demonstrate the dose-dependent effect of colcemid and colchicine which may be of interest to physicians encountering irradiated patients. So, the study examined the effect of phytohaemagglutinin (PHA) and colcemid or colchicine dose concentrations on DNA repair capacity and chromosome aberration yields in human blood lymphocytes exposed to ionizing radiation. Whole blood samples were irradiated with (2 Gy) γ-rays. PHA (0.2 ml) was added to blood cultures either immediately after irradiation or after a certain recovery period (1 & 2 h). In the second part of the experiment, we used both colcemid and colchicine with 2 different concentrations (0.025 & 0.05 μg/ ml). The number of dicentric chromosomes and acentric fragments were significantly increased in lymphocytes stimulated by PHA immediately after the irradiation. On the other hand, the use of colcemid with dose range 0.025 to 0.5 μg/ ml is better than colchicine with the same doses in the accurate estimation of the absorbed radiation dose.