Cardiovascular studies on conscious laboratory animals are required for an accurate assessment in drug evaluations. However, attempts to define pharmacological significance of an agent in conscious and unrestrained animals have been limited by the techniques available for recording the cardiovascular parameters. We designed a system which can be applied to record biological pressure, such as the blood pressure, using a miniature FM-FM radio-transmitter and a receiver demodulator. The transmitter consists of a differential amplifier capable of an input signal up to 3 X 10(6) times, voltage controlled oscillator which triggers a 2-5 volts range and 76-90 MHz transmitting oscillator. The transmitter requires a 5.6 V mercury battery. Earphone output of a commercial FM radio-receiver serves for signals to the demodulator. The demodulator is based on the phase locked loop principle and is equipped with an independent output for instantaneous wave recording and the mean of this recording. Transmitting distance of the system may depend on the receiver, however, in most instances, the distance is over 39 meters, in an open field. Accuracy of the telemetering data is dependent on discharge characteristics of the mercury battery. After discharging 5%, the full capacity of the cell gives a sufficient zero stability and accurate pressure measurements.