The distortion effect that the nonuniform equatorial electrojet (EEJ) currents might have on the plane-wave assumption in magnetotelluric (MT) applications is investigated under experimental conditions. A broad-band (0.0006-2048 s) MT survey, consisting of 8 stations aligned at right angles to the magnetic equator and probing diverse geologic terrains, was carried out during the daytime, under the presence of the EEJ nonuniform source, and at nighttime, when the EEJ flux almost vanishes. A comparison between the daytime and nighttime soundings did not show any significant divergence, contrary to expectation from some theoretical calculations. Thus, the results assure that the traditional plane-wave formula employed in MT can provide reliable subsurface conductivity structures even under the influence of the EEJ, at least up to periods of 2048 s. An additional modelling exercise considering the two models most commonly used to simulate the EEJ sources was also performed. It indicates that the line-current model generates departures from the plane-wave results not observed in practice and that the Gaussian model only agrees with the experimental data, within their error bars, if the geoelectric section approaches its most conductive limit defined from a static shift evaluation.¿ 1997 American Geophysical Union