Under the application of high shear rates, concentrated suspensions of colloidal particles jam. The stress necessary to induce their flow abruptly increases and exhibits very large fluctuations. At the transition, the first normal stress difference increases and develops fluctuations. The sign of the first normal stress difference changes with the volume fraction of the suspension, which becomes dilatant at high volume fraction. I review an experimental study of this jamming transition and experimental evidence of the dilatancy of the suspension.