Ion mass spectrometer observations of low-temperature streaming plasmas in the earth's magnetotail are reported. Measurements in the energy per charge range 0?E/q?17 keV/e were made at geocentric radial distances <23 RE from the ISEE 1 spacecraft. Ion streams of solar wind origin in the magnetotail boundary layer and of ionospheric origin in the tail lobes and plasma sheet are described. A statistical study of some of the characteristics of the streams allows us to infer that the central tail plasmas are primarily primarily constituted of ion streams of ionosphere is a significant contributor to the hot plasmas that form the plasma sheet.