A Cu-SAPO catalyst for NH3-SCR applications showed a significant loss of deNO(x)performance after exposure to oxygen-free conditions. The present work aims at elucidating the causes of the observed progressive deactivation by comparing different experimental procedures for the SCR activity tests. The adoption of an experimental protocol, which avoids the exposure to a non-oxidizing environment, ensured a stable activity of the Cu-SAPO catalyst. Moreover, treatment of the deactivated catalyst with an oxidizing mixture at 550 degrees C for 5 h enabled to partially recover the deNO(x) activity.