Abstract: The blood collecting syringe is constructed for coupling with an arterial blood sampling system. In one embodiment, upon retraction of a plunger, a collapsed hollow deformable stopper expands to draw any air bubble and fluid into a small discard chamber within the stopper. Continued retraction of the plunger causes the stopper to also retract thereby forming a specimen collecting chamber within the distal end of the barrel for receiving whole blood from the sampling system. In another embodiment, the plunger has a cap mounted within a hollow stopper so that upon movement of the cap from a forward position within the stopper to a retracted position within the stopper, a discard chamber is formed within the stopper while at the same time, any air bubble and fluid is drawn into the discard chamber. Subsequent movement of the plunger also causes retraction of the nozzle thereby opening up a blood specimen collecting chamber.