Summary The paper describes a modified splitting test by means of which it is possible to trace the complete load deformation characteristics of plain concrete loaded beyond the nominal splitting load. It is known that concrete will not exhibit a sudden brittle tensile failure provided the deformation is adequately restrained in some way. In this test, the restraint is provided by a steel beam acting in parallel with the concrete specimen in resisting the load applied by the testing machine. The applied load is carried partly by the concrete and partly by the steel in relation to their respective stiffnesses. As the load increases, the steel carries a higher proportion, and it is possible to extend the test on the concrete into the region where its portion of the applied load decreases as the deformation increases, that is, into the zone of negative stiffness.