We analyze wave and particle data from the CRRES satellite to determine the variability of plasmaspheric hiss (0.1 500 nT), with an average amplitude of 40 ¿ 1 pT observed in the region 2 15¿) hiss is strongest during active conditions with an average amplitude of 47 ¿ 2 pT in the region 2 < L < 4 from 0800 to 1800 MLT but extending out beyond L = 6 from 1200 to 1500 MLT. Equatorial hiss at 600 Hz has minimum cyclotron resonant energies ranging from ~20 keV at L = 6 to ~1 MeV at L = 2, whereas midlatitude hiss at 600 Hz has minimum resonant energies ranging from ~50 keV at L = 6 to ~2 MeV at L = 2. The enhanced equatorial and midlatitude hiss emissions are associated with electron flux enhancements in the energy range of tens to hundreds of keV, suggesting that these electrons are the most likely source of plasmaspheric hiss. The enhanced levels of plasmaspheric hiss during substorm activity will lead to increased pitch-angle scattering of energetic electrons and may play an important role in relativistic electron dynamics during storms.