The effects of pressure p, voltage v and interelectrode distance d on the production of active nitrogen by a high-frequency discharge have been examined simultaneously with the study of its physical and spectral characteristics. The results show that afterglow intensity I is a smooth function of p, v and d. The (I, v) curves have intensity maxima I_max, and a plot of I_max against p³ gives a linear relation indicating a three-body mechanism. Activation is poor when the discharge has strong N₂⁺ bands, or has bands of Gaydon's S, or Kaplan's second or fifth positive systems, characteristic of a condensed discharge. Stanley's short-duration afterglow has also been produced.