We analyze the auroral electrojet index for the days 30-31 October 1978 as the output of a nonliner system driven by vrious aspects of the interplanetary magnetic field (IMF) and solar wind (speed and density). The nonlinear input/output analysis takes the form of a prediction scheme; we compare the results to an autoregressive (linear) predictor and to a nonlinear predictor based only on the output signal. Different combinations of the solar wind variables are used as input functions. We find that only a few of the input combinations show any evidence whatsoever for nonlinear coupling between the input and the output for this interval. ¿ American Geophysical Union 1994