A single-use hypodermic syringe which locks up after one use. There is a body having a cylindrical container for holding a fluid. A hollow needle communicates with an interior of the cylindrical container through one end and a sliding plunger disposed in the cylindrical container is connected to a plunger rod disposed through an opposite end of the cylindrical container. There is locking apparatus allowing the plunger to move only in a direction towards the one end whereby after the plunger is moved adjacent the one end, it cannot be withdrawn for subsequent use. In one version, the plunger has a locking plate attached thereto. In another version, a hooked plate at the end of the cylindrical container digs into and grips an end bore of the plunger. In still another version, the plunger rod is gripped and held if movement to withdraw the plunger is attempted. Both disposable and carpule-using versions are disclosed.