Telemetric recording systems offer the advantage to monitor physiological parameters in freely moving animals without any restrictions in their explorative behaviour. We present a novel, inexpensive, portable and reusable telemetric system to record the electroencephalogram (EEG) from adult freely moving rats under various experimental conditions. Our system consists of an implantable transmitter which communicates at a sampling rate of 500 Hz bi-directional with a receiver via radio transmission (in EU: 868.35 MHz; in USA: 916.5 MHz) over a distance of up to 3m. The switching time between receiving and transmitting signals is 20 mus and the data transmission rate amounts to 115.2 kbps. The receiver is connected to a laptop via an USB connection and the data are displayed and saved by a software developed by the authors. This system allows the simultaneous recording and storage of a video signal for direct comparison of the animal's EEG with its behaviour. EEG recordings could be obtained over 4-5 weeks and under various experimental conditions (i.e. from rats swimming in water). The current system is optimized for recording electrical activity from the animal's brain, but can be easily modified to record other physiological parameters.