In the last few years (after 1976) new instruments have been used for plasmaspheric studies (‘mutual-impedance’ probe, ion energy-mass spectrometers) which have led to new results. The existence in the plasmasphere of previously unknown ions (He2+, O2+) was revealed and the pitch-angle distributions of ions with energies 10–20 eY were measured. New measurements confirmed the existence of a ‘hot’ (‘warm’) zone in the outer plasmasphere and of a midday-midnight asymmetry of the plasmasphere. The source of outer plasmasphere heating is apparently the ring-current decay; electrons are heated less than ions. The plasmasphere is not only the medium of ring current decay, but it appears that it is one of thering-current ion sources.