Without invoking the whistler hypothesis, but assuming they are not man-made it is shown (1) that the 100 Hz electric fields observed on the Pioneer Venus orbiter in the lower ionosphere (below 160 km, at night) can be so intense that they would produce unrealistic heating and depletion of the ionosphere, if they existed on a planetary scale; and (2) assuming the signal is not electrostatic, their accompanying magnetic field b at high intensity would be greater than the ambient field. Similar conclusions follow from invoking linear theory at whistler frequencies to explain the signal. Nonlinear theory would be needed to describe the propagation, if whistlers are the cause of the high-intensity signals, but this would not overcome the heating problem. Previous conclusions based on linear theory would be invalid for these high-intensity signals. In addition, for the most intense electric fields at 129 km altitude the ionization produced by the intensely heated electrons would be excessive. It is concluded that the 100 Hz signals can not be due to whistlers, or electromagnetic waves of planetary scale, and therefore these signals could not be used to support the case for lightning on Venus. These arguments favor the hypothesis that the 100 Hz electric fields are highly localized to the spacecraft. ¿ American Geophysical Union 1996