Trapped protons in the outer radiation belt of the earth can be removed through charage exchange by collisions with neutral exospheric hydrogen. The neutralized energetic particles escape into interplanetary space as well as to low alitudes. At low altitudes these particles constitute a copy of the outer radiation belt and have been repeatedly observed. It is proposed that the energetic neutral hydrogen escaping into interplanetary space is responsible for the recently observed highly anisotropic hydrogen flux at energies 0.29--0.5 MeV during solar quiet time. The expected energy spectrum of the neutral hydrogen flux in interplanetary space is derived from low-altitude measurements obtained on board the Esro 4 satellite and is compared with the observations. The result supports the hypothesis.