A needleless device for introducing or withdrawing a fluid to/from the vascular system of a being. The device includes first and second housing sections movably connected with respect to each other and which define a hollow interior in which a pair of resilient valve elements are located. The first housing section includes a first luer fitting for connection to an input line. The second housing section includes a second luer fitting for connection to an output line. A tubular plunger is located within the device and is arranged, when the housing sections are in a first position, to be automatically extended through a first valve element if the input line is connected to the first luer fitting, so that a liquid can be forced from the input line through the device to the output line. When the housing sections are in the first position and the input line disconnected from the first luer fitting, the tubular plunger is retracted out of both valve elements so that the device is fully occluded. The housing sections are movable to a second position with the input line connected to the first luer fitting, whereupon the tubular plunger is extended through both valve elements to provide free fluid communication between the input and output lines.