A teaching file is of paramount importance for a teaching department. It should be easily accessible and readily available. Considerations of costs and available space influence the choice of film size for the copies. We have chosen for 10 X 10 cm copies, because the majority can be viewed by individuals on normal lightboxes, while for larger audiences various ways of projection are feasible. The possibility, offered by the Delcomat copying apparatus, of making copies of interesting parts of the original film in varying degrees of reduction in size, enhances the practicability of the method.