The response of the near-earth magnetotail to a sharp and isolated northward turning of the IMF observed at the WIND spacecraft is studied in the near-Earth plasma sheet at x=-19 Re. Because of the possible time coincidence this northward turning could be causally related to an onset of the substorm expansion phase where Bz increased and the earthward convection intensified in the plasma sheet. The changes in the flow velocity and Bz to lower values occurred about 30 min later but they were not associated with an expansion phase onset. Thus the observations do not support the suggestion that the northward IMF turning produces a tailward sweep of the reduced dawn-to-dusk electric field and thereby triggers the substorm onset.¿ 1997 American Geophysical Union