© 2019, The Psychonomic Society, Inc. Two experiments investigated positive priming and negative priming effects in a lexical decision task. A priming task was used in which participants were required to make a verbal naming response to a prime target word, flanked by a distractor word, followed by a lexical decision response to a probe target word or nonword, flanked by a distractor word. The longevity of both positive and negative priming was explored in short-lag and long-lag conditions in which stimuli were presented once and only once, except in order to fulfill the priming manipulations. The results showed significant immediate positive priming and negative priming effects, but only negative priming was sustained for over 8 minutes with many intervening trials, whereas there was no evidence of positive priming after the same delay. These intriguing results have implications for the nature of inhibitory processing and differing predictions between inhibition-based and episodic retrieval accounts of priming.