A thesaurus of terms for indexing the literature of mineral processing and metals extraction is now available from the Warren Spring Laboratory, the Department of Industry's Research Establishment at Stevenage. Covering 150 pages of invaluable reference information for all workers in these fields, the thesaurus has been developed from the terms used for indexing articles of interest to the Mineral Processing and Metals Extraction Divisions of the laboratory since its inception in 1959. In 1966 fixed subject (‘concept’) headings were established each with its own corresponding fixed-length concept number. Development of this thesaurus as a working tool over a number of years has enabled many initial difficulties to be solved.