Abstract: An infuser for infusing a liquid from a reservoir, comprising a durable part (1,2,3) forming a housing and a disposable part (4) containing the liquid reservoir and an energy reservoir for energizing the pumping function. The infuser, further, contains in its disposable part (4) all liquid-contacting elements of the device, and the disposable part (4) and the durable part (1,2,3) are provided with mating coupling means (10,11).A controlling unit in an electronic compartment (3) of the durable part (1,2,3) has a socket (12) into which a plug (13) may be inserted, the plug (13) contains a ROM carrying information defining infusion data. The plug (13) has a transparent sheet (14) covering a display (8) of the durable part when the plug (13) is inserted in the socket (12). The sheet (14) carries a graphic representation of the information in the ROM to be seen in relation to information displayed on the display (8).