With the increased use of mobile phones, their biological and health effects have become more important. Usage of mobile phones near the head increases the possibility of effects on brain tissue. This study was designed to investigate the possible effects of pulse modulated 900 MHz and 1800 MHz radio frequency radiation on the permeability of blood-brain barrier of rats. Study was performed with 6 groups of young adult male and female wistar albino rats. The permeability of blood-brain barrier to intravenously injected evans blue dye was quantitatively examined for both control and radio-frequency radiarion exposed groups. For male groups; Evans blue content in the whole brain was found to be 0.08 +/- 0.01 mg% in the control, 0.13 +/- 0.03 mg% in 900 MHz exposed and 0.26 +/- 0.05 mg% in 1800 MHz exposed animals. In both male radio-frequency radiation exposed groups, the permeability of blood brain barrier found to be increased with respect to the controls (p < 0.01). 1800 MHz pulse modulated radio-frequency radiation exposure was found more effective on the male animals (p < 0.01). For female groups; dye contents in the whole brains were 0.14 +/- 0.01 mg% in the control, 0.24 +/- 0.03 mg% in 900 MHz exposed and 0.14 +/- 0.02 mg% in 1800 MHz exposed animals. No statistical variance found between the control and 1800 MHz exposed animals (p > 0.01). However 900 MHz pulse modulated radio-frequency exposure was found effective on the permeability of blood-brain barrier of female animals. Results have shown that 20 min pulse modulated radio-frequency radiation exposure of 900 MHz and 1800 MHz induces an effect and increases the permeability of blood-brain barrier of male rats. For females, 900 MHz was found effective and it could be concluded that this result may due to the physiological differences between female and male animals. The results of this study suggest that mobile phone radation could lead to increase the permeability of blood-brain barrier under non-thermal exposure levels. More studies are needed to demonstrate the mechanisms of that breakdown. (C) 2015 Elsevier B.V. All rights reserved.