The increased use of mobile phone worldwide has focused interest on the possible effects of radiofrequency fields on health. However, until now no satisfactory mechanism has been proposed to explain the biological effects of these radiations. Thus this study was undertaken in order to investigate the effect of radiations emitted from mobile phone on: Malonyldialdehyde [MDA], as a lipid peroxidation product, and serotonin concentrations, as well as the activities of acetylcholinesterase [AChE] and sodium-potassium ATP-ase [Na⁺ K⁺ ATP-ase] enzymes in the different parts of rats' brain. The study was conducted on twenty adult male albino rats. Ten were exposed to radiations emitted from cellular phone [the experimental group] and ten rats were in the same exposure conditions but the mobile phone was turned off [the control group]. NA⁺ K⁺ ATP-ase enzymatic activity was significantly lower while MDA and serotonin concentrations were significantly higher in all studied brain parts of the experimental group. AChE was found to be significantly lower only in the cerebellum of the experimental group. These results support the interaction of radiofrequency fields of mobile phones with biological systems. Oxidative stress and diminished NA⁺ K⁺ P-ase enzymatic activity in addition to disturbance in serotonergic neurons and possibly cholinergic neurons, all may play a role in the mechanism of adverse effects of electromagnetic radiations. Further studies are needed so as to find the threshold level for exposure to electromagnetic filed [EMF] that is not adverse to human health.