Short-term retention of individual trigrams was tested in blocks of 6 tests with within-block intervals of 5 or 16 sec. and 91 sec. between blocks. Recall at retention intervals of 0, 3, and 9 sec. was tested. Recall at the 9-sec interval was a direct function of interest interval. Intrusions of a letter from the previous trigram at a specific position was inversely related to time between tests. The problem posed for interference theory by a decline in proactive interference over a rest interval was considered. (PsycINFO Database Record (c) 2006 APA, all rights reserved)