Abstract: A method of distributing particles in a flow of gas and a needleless syringe for use in the needleless injection of particles into the skin or mucosa of a vertebrate subject are disclosed. The syringe includes a convergence which reduces pressure of the gas flowing in the gas flow path due to the Venturi effect such that particles initially located outside of the gas flow path are drawn into the gas flow path under the action of the reduced pressure and become entrained in the gas. An exit nozzle accelerates the particles so entrained. In another aspect of the invention, there is provided a method of creating a gas flow in a needleless syringe which comprises flowing gas through a first convergence into a chamber to form a transsonic gas jet in the chamber and passing the gas jet from the chamber into a second convergence and along the nozzle.