Evidence provided by the Dainton Report indicates that special libraries in the UK are far from fully exploiting the photocopying services provided by the national libraries. As these photocopying services are legally obliged to operate at cost, they offer significant economies to any special library which exploits them systematically. This paper describes a simple graphical method of estimating the savings that can be made, or the extended subject coverage that can be obtained at no additional cost, by substituting photocopies for relevant papers in the peripheral periodicals relating to any well‐defined scientific or technical subject. Though photocopying charges must be realistic, the confident exploitation of the national photocopying services depends on the avoidance of arbitrary jumps in photocopying charges.