Ramsar is a northern costal town in Iran. There are some hot sprigs in special areas in the town (Talesh mahalleh, Chaparsar and Abeseiah), which consist of 226Ra and 222Rn. The γ ray effect on the inhabitants and evaluation the inhabitant’s radiosensitivity or adaptive responses by in vitro method was studied. Vitamin C is an antioxidant and is known as free radical scavenger. It is believed that there must be relation between the level of vitamin C with radiation resistance and repair of damage. So the urinary level of Vitamin C has been evaluated. In this study one group of volunteers from the high natural background radiation areas were chosen as the case group and two groups of volunteers in normal background radiation areas of Ramsar and Tehran as control. The peripheral blood mononuclear cells (PMNCs) were separated and irradiated with 5 different doses (0،0.3، 1، 2 and 4 Gy) of γ ray from 60Co source. To evaluate DNA damage, single cell gel electrophoresis (comet assay) was used. In this technique DNA fragments immigrate in an electric field, and their footprint shows the amount of damage. It is elucidated that the damage is proportional on the absorbed dose. Evaluation of the urinary ascorbic acid was done with using of spectrophotometer On the whole, the results have revealed that DNA damage for the case group was significantly higher than both control groups (P<0.05). Subgroup of the case volunteers who lives in the areas with lower background radiation Ramsar; 10 mSv y-1, have shown less damage and more repair in comparison with those who live in very high background radiation; more than 10 mSv y-1 (P<0.05). The urinary vitamin C level in case group was less than control group from Ramsar. In conclusion the inhabitants in high background houses are radiosensitive and they are susceptible to DNA damage exposed to challenging dose. Subgroup with lower background radiation shows less damage and more repairs. It can be attributed to an adaptive response in t
