A microcomputer (with 8088 or 80286 processor)-based, R-wave triggered system for on-line, semi-continuous measurement of blood flow of one or two limbs, simultaneous with heart rate and eventually intra-arterial blood pressure, is described. The minimal interval between measurements is approximately 4 s, allowing the accurate measurement of maximal flow after ischemia. When compared to hand-operated plethysmography, the use of this system improves the precision of the measurements, minimizes perturbations of the limb circulation and eliminates the possible bias of analysis by hand.