This paper describes a system of diagonal beam reinforcing for reinforced concrete ductile frame buildings in seismic areas. The development and application of the system is described with reference to the design of an 18 storey building. The proposed reinforcing system has a number of major structural advantages over conventional reinforcing. Moments and shears within the beam span can be resisted entirely by the main reinforcing. Plastic hinge lengths are substantially increased and the hinging is kept away from the column face allowing concrete strut action to be effective in resisting forces within the elastic beam column joint.