Two experiments using a conditioned suppression procedure with rats found that following training, nonreinforced presentations of an inhibitory feature stimulus (X) had different effects, depending on whether a serial (A+, XA−) or a simultaneous (A+, A→X−) feature negative discrimination procedure was used to establish the inhibition. Those presentations exhanced X's inhibitory power after simultaneous feature negative training, but reduced X's inhibitory power after serial feature negative training. These data suggest that the nature of inhibition established in feature negative discriminations depends on the temporal arrangement of stimuli.