This paper discusses the wind tunnel tests conducted for the construction of the main span of the Pont de Normandie, presently being erected in France, to be the world's longest cable-stayed bridge. The paper describes the wind tunnel investigations conducted in the ''Martin Jensen'' very large wind tunnel at the Danish Maritime Institute (DMI) on a 1:150 scale aeroelastic model of the structure in its most vulnerable stage, when two unprecedented 420 m cantilevers will span the Seine, just prior to the erection of the last steel box girder joining the two halves of the bridge. This paper gives a detailed description of the aeroelastic model and presents a summary of the main findings. A companion paper [J. Wind Eng. Ind. Aerodyn. 65 (1996) 189-201] compares the measured responses to analytical predictions using state-of-the-art prediction methods.