An introducer sheath assembly (10) having a sheath tube (12), a hub (16), a valve (30) and a valve-retaining cap (50) on the proximal end of the hub. The cap (50) is so secured to the hub (16) as to have a closed, locked position and also an open position permitting access to the interior of the hub and the valve (30) while the cap (50) remains secured to the hub (16).