Described are a method and device for needleless injection of a liquid substance in the skin or other target tissue of a patient, in which droplets of the liquid substance are produced, and the droplets of liquid substance are directed toward the surface of the patient's skin or other target tissue at a velocity sufficiently high to inject the droplets of liquid substance in the patient's skin or other target tissue. The droplets of the liquid substance are accelerated toward the surface of the patient's skin or other target tissue in order to inject the accelerated droplets of liquid substance in the patient's skin or other target tissue. A high velocity jet of gas is produced, droplets of the liquid substance are produced and supplied in the high velocity jet of gas, the droplets of liquid substance are conveyed within the high velocity jet of gas, and the high velocity jet of gas is guided toward the surface of the patient's skin or other target tissue in order to inject the conveyed droplets of liquid substance in the patient's skin or other target tissue.