Good agreement is obtained between the calculated and the observed O+, N2 +, and N+ ion distributions for an aurora with a peak electron concentration of about 1.1¿106 cm-3 near 110 km. The NO profile required to explain the NO+ and O2 + data is deduced and discussed. The inferred peak nitric oxide concentration is among the three largest (all about 109 cm-3 values ever derived in studies of over a dozen Air Force Geophysics Laboratory auroral rocket flights.