Since neutrons constitute a numerically important component of the cosmic radiation [see 1 of “References” at end of paper], the question arises as to the amount of ionization in the atmosphere at sea-level which they produce. This ionization will be produced in two ways: (a) By recoil-nuclei produced by the neutrons in collisions; and (b) by the ionizing radiation ejected from nuclei as a result of neutron-induced disintegrations. We may set limits to each of these contributions.It is believed that most of the neutrons in the atmosphere at sea level are evaporated out of nuclei by the high-energy cosmic radiation, and have initial energies of 10 to 30 Mev. It has been pointed out by Bethe, Korff, and Placzek  that these neutrons will first be inelastically scattered by nitrogen nuclei. In this process, the neutron enters the nitrogen nucleus, causes the ejection of one or more nuclear particles, and usually emerges with about four Mev energy. The bulk of the energy of the neutron is used in breaking up the binding of the nucleus, and hence is not transformed into ionization. The ionizing particles which are emitted will in general have energies which are small compared to the initial energy of the neutron, and it may be estimated  that of the order of five Mev per neutron will appear as ionization.