Although first developed 150 years ago, it is only within the last 25 years that facsimile transmission has had widespread use. Its use for document supply is limited to the last 10 years when the CCITT group III standard was ratified. The British Library Document Supply Centre (BLDSC) carried out a trial in 1983 and subsequently added facsimile document transmission as part of its Urgent Action Service. Group III transmission has limitations for document delivery applications. These are discussed along with the advantages and disadvantages of group IV transmission. Details are also given of a trial of group IV transmission between BLDSC and University College in London.