A pre-slit injection site (34) includes a housing (40) with a flow path therethrough. A first end (42) of the housing (40) carries a pre-slit septum (52). One form of a blunt cannula (98), usable with the injection site (34), carries a locking member (100). When the pre-slit injection site (34) slidably receives the blunt cannula (98), the locking member (100) latches to the injection site (34) and creates a mechanically coupled unit. Another form of the cannula (280) includes a tube having a tapered distal end region (298) and having elongate discharge slots (294) for reducing contact surface area and for directing the flow laterally out of the cannula. The cannula may also include a rounded lead post (330), an annular barb (394), and axially oriented grooves (268). A blood sampling system utilizing an in-line pre-slit injetion site (492) and a shielded blunt cannula (512). An adapter for transferring fluids from a syringe with a blunt cannula to an evacuated tube, including a pre-slit injection site (554) and a shroud covered needle (556) with a rubber sleeve.