There has been a tendency in recent years to give larger doses of contrast in intravenous urography and a dose of 50 to 60 ml. is now routine in many departments. If dosage is related to body weight of the order of 0·5 to 1 ml./kg as indicated by Sherwood, Breckenridge, Dollery, Doyle, and Steiner (1968), the heavier patient may well require a dose of 90 ml. or more. As the manual injection of 50 ml. or more of contrast requires a not inconsiderable physical effort and may have to be given in two separate syringefuls, there appears to be a strong case to the introduction of some form of mechanical injector. To this end, the spring-operated injector was evolved (Fig. 1). The apparatus consists of a metal base plate and two slotted side plates, which house the supports of a pressure plate; a spring is attached to each support of the pressure plate and to an anchor at the front of the base plate. A syringe clamp is located about midway along the base plate and a further tubing clamp is located in front to hold the tubing of an infusion set. The apparatus will accept either a 100 ml. glass syringe or a 50 ml. plastic syringe for which a collar is provided, to enable it to be fitted into the syringe clamp. Construction was carried out at 43, Command Workshops, R.E.M.E., Aldershot.