The deformation of the paper web during and after a suction pulse on initially saturated fibre web made of chemical and mechanical pulp was investigated. A laboratory suction box was used, where the suction time and pressure drop could be varied and controlled. During the experiments, the web thickness, the air flow through the web and the suction pressure were recorded and after the experiments, the dry content of the web was determined. A large deformation was observed when the suction pulse was applied. After the suction pulse, a considerable expansion of the web took place, probably an effect of rewetting. The compression of the web appeared to be the most important dewatering mechanism increasing the dry content of the web. However, if the web is not separated from the forming fabric, rewetting after the suction pulse will greatly reduce the dry content.