An assembly of parts (10) for an endourological procedure, comprising an elongate tubular sheath (1) and an elongate introducer (2), the tubular sheath being removably mounted on the introducer. The tubular sheath comprises at least a first (21) and a second (22) lumen, at least the second lumen being openable to shift a guidewire from a position inside the second lumen to a position outside and next to the tubular sheath. Disclosed are also access sheaths.