Abstract: An intravenous catheter insertion set and blood sample gathering unit are combined to allow catheterization for intravenous medication and gathering of blood samples from the same venipuncture site. A hypodermic needle and a vacuum container needle protrude in opposite directions from a hub. A catheter is carried by the hypodermic needle. The hub includes a flashback chamber, vented to allow blood to flow into view within the chamber following proper venipuncture. The vent is selectively sealed as the plug end of a vacuum container is pierced by the vacuum container needle. Blood is then drawn into the tube by vacuum pressure. When a sufficient sample has been taken, the needle assembly is withdrawn, leaving the catheter in place.