British Telecom is planning the introduction of an integrated services digital network, designed to carry data, text and voice. The Kilostream services will provide a dedicated data network that will support synchronous data transmission at datarates from 2 400 bit/s to 48 kbit/s, using both X.21 and X.21bis customer interfaces. The paper examines the planning of the system, equipment realization and the network applications being considered. Future developments of the Kilostream concept are also discussed.