Counterstreaming ions or ions traveling simultaneously both parallel and antiparallel to the magnetic field direction have been briefly noted in the literature but have not been studied previously in depth. We have studied over 60 counterstreaming ion (CSI) events observed on the ISEE 1 satellite. Often, both oxygen and hydrogen ions at a number of energy levels are counterstreaming, but some events show only either oxygen or hydrogen ions at one or more energy levels involved. One particularly interesting event shows only counterstreaming oxygen ions with 417 eV energy; oxygen ions of lower energh (215 eV) and higher energy (630--17,000 eV) and all the hydrogen ions between 215 and 17,000 eV energy have lower fluxes and/or nearly isotropic pitch angle distributions. This event correlates well with wave activity in the 17- to 100-Hz band and is also accompanied by 200-eV downgoing and 400-eV upgoing electrons. Details of this and some other CSI events are presented. The CSI events were found to occur at altitudes of about 2--8 RE on L shells of about 5--12 in the evening-to-morning sector from about 1700 to 0900 LT; the majority of the CSI events at altitudes between 2 and 5 RE and L values from 5 to 8 involve oxygen ions, while at higher altitudes from about 5 to 8 RE and higher L values from about 8 to 12 the majority involve hydrogen ions. Some features suggest wave-particle interaction may be involved in some CSI events. ¿ American Geophysical Union 1987