A sampling port (10) has a body (12) having an space (35) open at one end (20) and adapted to receive a sampling vial (70) with an cannula (24) extending longitudinally along the space (35) with a pointed end (26) facing the open end (20), whereby a sampling vial passed into the space from the open end may be impaled on the cannula. The port includes at least one guide member (36) extending into the space (35) to reduce the effective size of part of the space (35), the at least one guide member (36) guiding a vial (50) of a first size when inserted into the open end (20) and the at least one guide member (36) being movable to allow a vial (70) of a size larger than the first size to be inserted into the space.