Background: Measurement of background radiation is very important from different points of view especially for human health. The aim of this survey was focused on determining the current background radiation in one of the highest altitude regions ( Zagros Mountains ), Chaharmahal and Bakhtiari province, in the south west of Iran .

Materials and Methods: The outdoors-environmental monitoring exposure rate of radiation was measured in 200 randomly chosen regions using portable Geiger-Muller and Scintillation detectors. Eight measurements were made for each region and an average value was used to calculate the exposure rate from natural background radiation.

Results: The exposure dose rate was found to be 28.4 m Rh^-1 and the annual average effective equivalent dose was found to be 0.49 mSv. An overall population weighted average outdoor dose rate was calculated to be 49 nGyh^-1, which is higher than the world-wide mean value of
44 nGyh^-1 and is comparable to the annual effective equivalent dose of 0.38 mSv.

Conclusion: A good correlation between the altitude and the exposure rate was observed, as the higher altitude regions have higher natural background radiation levels. Iran . J. Radiat. Res.; 2003; 1(2): 87 – 91.