Energetic neutral particles resulting from the charge exchange of ring current ion with geocoronal hydrogen are known to strike the atmosphere at low latitudes. We have evaluated the ionization rates caused by these particles in the low-latitude upper E region ionosphere. We find that these particles are an important quiet time source of E region ionization at night and that they can account for the observed increases in nightime ionization that correlate with geomagnetic activity. This ionization has previously been attributed to 1- to 10-keV electron precipitation. However, sufficiently intense precipitating electron fluxes have not been measured at low latitudes, and we know of no source of such electrons.