Attention is drawn to the possibility that H + HO2 → H2 + O2 may be an important source of hydrogen molecules in the lower thermosphere. It is suggested that the fractional volume abundance of hydrogen atoms (free and combined) in this region is determined by, and is not very much less than, the corresponding fractional volume abundance in the stratosphere. Any hydrogen molecules in the lower thermosphere would affect the altitude distribution of hydrogen atoms and augment their rate of escape. © 1965.