Conducted 2 experiments with 75 and 45 male blue spruce hooded rats to evaluate various response prevention procedures of extinction when cs exposure/trial was held constant. Preventing the occurrence of a response resulted in a low activity level for ss during prevention trials and rapid extinction of the conditioned avoidance response (car). S's activity level and car extinction also appeared to be related to instrumental response contingencies and where the iti was spent. Fear extinction occurred during response prevention and appeared to occur in direct proportion to the total amount of cs exposure, irrespective of s's activity level during the cs exposure, number of trials, or the instrumental contingencies involved. (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1971 American Psychological Association.