A self-contained automated system for venous occlusion plethysmography is described. The system is microprocessor controlled and performs the complete venous occlusion plethysmographic process of measurement, analysis and printout of results at the command of two keypresses on a keypad. Limb circulation is modelled by a linear model. Limb volume change is measured by electrical impedance plethysmography. The system is convenient to use clinically, either for the measurement of blood flow in the legs or for the diagnosis of venous thromboembolic disease. The hardware and data processing software of the system are described and examples from clinical use of the system are presented.