An assembled blister package (1) has a blister sheet (11) formed with blisters (2) sealed by a foil backing sheet (4). The blister package (1) is sandwiched between opposite sides of a folded card (not shown) to stiffen it. Each of these sides has a rectilinear array of windows, the blisters protruding through one array of windows and the other array of windows defining discrete areas on which print describing the contents of the blisters beneath, is to be applied. A header sheet on which a bar-code is printed is attached to the backing sheet and a reader (23) is positioned to read the bar-code and extract from it information such as a description of the contents of each of the blisters and their respective positions in the package. Information relating to the identification of the contents of a particular blister and the identity of the patient is fed to an ink-jet printer (31) and two stepping motors (22 and 30) are used to control the position of the printer with respect to the backing sheet. As the printer does not make physical contact with the backing sheet, it can be spaced from it by a sufficient distance to enable it to pass over the card without obstruction despite the card being salient with respect to the surface of the backing sheet. Printing can thus proceed quickly without obstruction by parts of the card and without having to vary the distance between the printer and the irregular surface over which it passes. This has the advantage that no precise alignment of the backing sheet with the blister sheet is necessary during assembly of the blister package, and problems associated with securing the backing sheet to the blister sheet are avoided. As the printing information is read from the bar code on the header sheet which is attached to the blister package, there is a direct correlation between the written description of the blister contents on discrete areas of the backing sheet and the patient identity information read from the header card as both ar
