Data from a low-orbiting satellite with a quasi-polar orbit have been studied to determine if man-made waves, such as the Power Line Harmonic Radiations (PLHR), can affect the intensity of the ELF waves observed in the ionosphere. The signals coming from two electric components were processed with a system of 6 filters (from 10 Hz up to 1000 Hz), and recorded on-board all around the Earth. Most ELF waves derived from electrostatic turbulence. It is shown that the signal recorded by the electric component that is parallel to the Earth's magnetic field has a modulation depending of the days of the week. The amplitude is maximum on Mondary and decreases until Saturday. The largest difference between Mondary and Saturday (93%) occurs with the filter centered around 72 Hz. The interpretation of the experimental results supposes that the intensity of the ELF waves is connected to the PLHR influence on the ionospheric plasma. A theory is presented to explain this variation: the PHLR emitted from the ground during weekdays are different from those of the weekend, not only because power consumption is lower, but also because the ground configuration of their sources is changed. ¿ American Geophysical Union 1991