Abstract: A disposable hypodermic syringe which is self-destructing upon a single use has an elongate, cylindrical barrel with an adapter means on one end for attachment of a needle and an open other end. A plunger and piston carried thereby are reciprocable in the barrel. The improvement comprises releasable, interengaged flange means on the piston and plunger for holding the piston and plunger assembled together during initial retraction of the plunger and piston in the barrel but which is operative to disengage the mutually engaged flange means upon forward movement of the plunger in the barrel, whereby subsequent retraction of the plunger results in separation of the piston and plunger, rendering the syringe inoperative for subsequent reuse.