A cannula introducing device comprises an elongate body (10) having a needle (12) projecting from a front end, an operating element (24) for displacement longitudinally of the body (10), a plunger (16) disposed at the front end of the body (10), and a coupling means (18), such as a flexible wire, coupling the operating element (24) and the plunger (16), arranged so that retraction of the operating element (24) serves to advance the plunger (16) over the needle (12) and so advance the cannula (30) which is disposed over the needle.
