Abstract: A measuring apparatus for the noninvasive determination of peripheral outflow and flow disturbances in the extremities of human beings includes at least one light transmitter for directing light onto the skin of the subject under test and at least one light receiver for receiving reflected radiation and an evaluation and read-out circuit for ascertaining the temporal course of the blood outflow or inflow in the veins by measuring the changes in light reflection. The evaluation and read-out circuit is provided with a digitally controlled tone generator and an electroacoustic transducer that emits a first signal to indicate readiness of the apparatus to effect measurement, a second succession of tones, the frequency of which follows the changes in the intensity of the light reflection until termination of the blood outflow or inflow, and a third signal which indicates the end of the measuring.