12 rats were tested for disinhibition after being trained on a fixed interval (FI) 3-min schedule. When a stable pattern of responding was achieved, a novel stimulus (buzzer) was introduced either for the entire duration of the schedule or for the 1st or last 1/2 cycle of the schedule. After 4 days of testing, the novel stimulus was removed and Ss were tested for recovery of the pretest behavior pattern. All groups, regardless of the temporal sequence of introduction of the novel stimulus, showed a marked disruption in scallop behavior on the 1st day of testing. Results are evidence of disinhibition in instrumental conditioning. (PsycINFO Database Record (c) 2006 APA, all rights reserved)