The principles and applications of local area networks (LANs) are now well publicised. They offer substantial advantages over conventional point-to-point links in a computer environment, since they impose little constraint on system configuration. Peripherals and processing nodes can be distributed on the network in any manner physically convenient to the user. The availability of complete cross-communication between stations permits distributed processing and shared access to storage and input/output media. In certain areas, however, conventional LANs have insufficient performance to cope with the traffic rate. Coupling a processor to main store via a LAN would be an absurdity; this clearly requires the use of a direct point-to-point interface. In some areas LAN flexibility is required, but at a performance level more typical of a dedicated link. This paper describes the implementation of a network which fulfils this requirement: MACROLAN. The transmission medium adopted is optical fibre and is thus a new technology serving a new application. The physical aspects of this network are therefore emphasised in this paper.