In order to comprehend the actual seismic behaviour of structures realized with new constructive technologies, a wide experimental programme has been carried out on lightly reinforced precast concrete - polystyrene sandwich panels, composed of a sheet of structural expanded polystyrene 160 mm thick inserted between two grids of galvanized and electro welded steel wire, completed by spraying concrete to form a composite structure. Experimental tests have been carried out on 16 panels set in the vertical position, in-plane loaded by constant vertical loads and at the same time subject to a cyclic horizontal concentred load. Results allowed the following parameters to be determined: the first cracking horizontal load, the load-displacement hysteretic curve, the collapse lateral displacement, the resisting shear at the bottom, the resisting moment considering P-delta effect, and the equivalent viscous damping coefficients.