An instrument which locates blood vessels by means of Doppler ultrasound and directs a needle at the located vessel has been developed. The feature of this instrument is that the needle does not pass down the ultrasonic beam as in other techniques that have been tried. Two transducers, mounted on sliding bars, are used to pin-point the vessel. The needle is then guided towards the itersection point of the two beams. Both the angle of entry and the point of incision of the needle can be chosen arbitrarily, while the transducers are kept well away from the needle and at an optimum angle to the skin.