Turbulence in the middle atmosphere is often investigated by assuming that the ionized component of the air acts as a passive scalar tracer for the neutral gas. This is the case for rocket-borne electrostatic probes in various configurations and for radar. It has long been accepted that the ions are not necessarily the faithful tracers one would like. Here we shall address the influence of the presence of negative ions on the turbulence spectra observed when positive ions represent the tracer. We shall see that departure of the spectral form from that expected for the neutral turbulence alone has considerable repercussions for observations, either in situ or remote, in the lower part of the mesosphere, and particularly in nighttime conditions when negative ion densities are greatest.¿ 1997 American Geophysical Union