A proposed instrument capable of measuring quantitative blood flow in man is described. The techniques utilized involve no trauma or hazard to the patient and, being transcutaneous, are suitable for clinical use. This report reviews the present status of transcutaneous blood-flowmeters, furnishes a brief tutorial on basic ultrasonic principles and limitations relevant to biological usage, considers the theoretical bases for the proposed techniques, and translates these into a prototype system. Finally, recommendations for initiating a program to devise such an instrument are presented.