Abstract: A single-use safety syringe assembly comprises an elongated, generally cylindrical barrel which forms a hollow nozzle located at the distal end of the barrel and which opens into the interior of the barrel. A plunger is slidably mounted in the barrel and forms a longitudinal cavity. A needle holder carries a hollow needle on its distal end, and the needle holder is slidably mounted in the longitudinal cavity of the plunger. A biasing arrangement urges the needle holder in a direction for retracting the needle into the barrel. However, a releasable latching arrangement retains the needle holder against the urging of the biasing arrangement in a position wherein the needle projects from the barrel. An In-Barrel assembly sequence is provided which permits sequentially inserting components of the syringe into the barrel and effecting assembly with a push of the plunger. An OTN catheter may also be employed in combination with the syringe assembly.