The injection of fluid substances through the human skin by means of a small jet at high pressure was shown to be feasible nearly 20 years ago.1 Since then several types of mechanical instruments have been devised that use this principle in the administration of certain biologicals. High pressures have been obtained by means of springs, solenoids, compressed air, carbon dioxide, or small explosive charges and with nozzles of various diameters. A wide variety of materials in volumes up to 1 ml. or greater have been inoculated by jet injection, including insulin, pituitary extract (Pituitrin), sulfones, antibiotics, vitamins, and anesthetics. These are described at length in the reports of Hingson and Hughes,2 Hirsh and co-workers,3 Hughes, Jordan, and Hill,4 and Hingson and Figge.5 The studies of Batson, Wall, and Landy6 first demonstrated the feasibility of administering a vaccine (typhoid) by jet injection.