This paper describes a computer-display method for interactive design of electricity-distribution networks. The display facility consists of a hardware character generator and storage tube, linked to an 8 K IBM 1130 computer. Thus the designer has an up-to-date network diagram to help him decide on the most suitable reinforcement plan. The designer can also call for information, such as substation data, relating to the network, and the results of both d.c. and a.c. analysis methods may be displayed in tabular form. A design study commences with the existing network, although authorised reinforcements which have not currently been installed may be included. Any proposed network is very easily studied for a wide range of operating conditions. Circuit outages may be considered, and bus loads can be increased for the purpose of load-flow studies in order to simulate load growth. The method is illustrated by a 22-node network which has been taken as an example from the MANWEB distribution system. Computation times for this network are short enough to suggest that the method can be applied to much larger networks. The designer's range of ideas is increased as a result of using this system, and he is therefore likely to obtain significantly improved designs over what present methods will afford.