A microcomputer system for the measurement of parameters of ventilation and blood pressure in the spontaneously breathing anaesthetized patient is described. The system continuously calculates minute volume, respiratory frequency, and mean end tidal carbon dioxide concentration. Additionally four cardiovascular parameters are measured. The inputs are obtained from a wet-wedge spirometer, a capnograph and a blood pressure monitor. The methods of computer calculation are described in detail. The computer-generated results are compared with those obtained by manual calculation. The system described has the capacity to record and display a wide variety of further measurements made during anaesthesia. This system provides invaluable information for research and teaching, but may also be useful during routine anaesthesia.