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Midlatitude sunrise electron density profiles have been analyzed in order to determine nitric oxide concentrations in the range 100–160 km. In general, the determinations are restricted to heights for which the ionization of nitric oxide by direct solar Lyman-α radiation is the main contribution to the growth of the E region. The concentrations obtained are larger, by factors of approximately 3 to 4, than those obtained from the midlatitude airglow measurements of other workers. Concentrations have been obtained from one sunset measurement and these are significantly lower than the sunrise values. The results also give a clear indication of increasing nitric oxide concentrations above 120 km with increasing solar activity.