Energetic (E>1.6 MeV, >3.9 MeV) trapped electron fluxes observed at the synchronous altitude during 1974 and 1975 by an experiment aboard ATS-6 exhibit a modulation in intensity which is correlated with the passage of sector structure boundaries of the interplanetary magnetic field past the earth. The electron fluxes reach equilibrium intensities during the time the magnetosphere is in a given IMF sector which are higher in the fall for (+) sectors and highest in the spring for (-) sectors.