Highly relativistic electrons are known to be present at synchronous satellite altitude in time-varying and sometimes large intensities; it is therefore important to consider the fluxes and locations of relativistic electrons precipitating into the atmosphere. Here we present measurements from the low-altitude three-axis-stabilized satellite S81-1 of trapped and precipitating electrons from 6 keV to above 1 MeV. Significant fluxes of precipitating relativistic electrons above 1 MeV within the bounce loss cone are much more often observed near midnight than noon and generally in narrow spikes1-MeV electrons has been measured to occur at intensities and in locations that are widely variable within a few minutes superposed on longer-term variations. On one of the days of strongest precipitation the total nighttime input to the atmosphere during 12 hours from >1-MeV electrons within the bounce loss cone near the trapping boundary was ~1019 ergs, which was an order of magnitude less than the loss rates estimated by Baker et al. from high-altitude measurements, suggesting that precipitation in the drift loss cone may be significant. ¿1991 American Geophysical Union