A device for non-invasively locating and marking blood carrying vessels in a live human body includes a housing having a control panel for user selection of functions, a central processing unit controlling said functions. The device includes motorized legs for regulating the height of the housing above a patient's skin according to data received from a proximity sensor. The device includes an upper carriage driven in a first direction and a lower carriage driven in a second direction that is perpendicular to the first direction. The lower carriage is coupled to the upper carriage such that the lower carriage can be positioned at any position within an x-y plane. The device further includes a transducer for locating the position of a blood vessel through the transmission and receipt of ultrasonic waves. The transducer is mounted to the lower carriage such that the path of a blood vessel can be tracked through carriage movements according to signals received by the transducer. When a vessel has been located, the vessel is tracked and the x-y coordinates are stored in sequential memory locations. The x-y coordinates are then used by a plotter attached to the lower carriage to mark the path of the vessel upon the skin of the patient.