The article reports on tests to failure carried out on negative-moment sections of five composite plate girders and a steel plate girder with slender stiffened webs. The study examines the interaction between tension-field action in web panels and the shear connection to the slab above for girders with relatively light steel top flages. The ultimate strength of all six girders exceeded by 30 per cent or more that given by the design method of the bridge code to BS5400. Details are given of a method of analysis, developed from other studies, that accurately predicts observed ultimate strengths. (Author/TRRL)