We tested the hypothesis that common stimuli are stored in memory better than bizarre stimuli are. Subjects memorized a series of noun pairs embedded within 20 common or bizarre sentences. By using a between-list design, free and cued recall, and intentional-learning instructions, we were able to obtain a commonness effect (Le., a recall advantage for the common sentences). Riefer and Rouder's (1992) multinomial processing-tree model for measuring storage and retrieval was applied to the data, which revealed that the recall advantage for common sentences was due to storage and not retrieval processes. We propose a two-factor theory: that common items are stored better in memory, but that bizarre items are retrieved better from memory. This storage-retrieval explanation does a good job of accounting for a number of fmdings associated with the bizarreness effect.The bizarreness effect is the observation that bizarre or unusual stimuli are remembered better than common or ordinary stimuli (Lang, 1995;Weir & Richman, 1996;Worthen & Marshall, 1996). Memory researchers have been investigating this phenomenon for over 25 years; yet experimental support for the bizarreness effect over this time span has been somewhat mixed. Early experiments (e.g., Andreoff& Yarmey, 1976;Senter & Hoffman, 1976) failed to show any recall advantage ofbizarre stimuli, and some studies actually showed a recall advantage for common stimuli, a phenomenon referred to as the commonness effect (e.g., Collyer, Jonides, & Bevan, 1972;Wollen, Weber, & Lowry, 1972). More recent studies have shown that, under the right circumstances, a reliable bizarreness effect can be obtained experimentally. Specifically, the effect is best achieved using free recall, mixedlist designs, incidental-learning instructions, and delayed recall (see McDaniel, 1987, andMcDaniel, Einstein, DeLosh, May, & Brady, 1995, for reviews).However, this recent work also reveals that the bizarreness effect is a fragile and complex one, requiring a very specific set ofexperimental conditions. For example, McDaniel and Einstein (1986) showed that the effect is obtained when subjects evaluate the vividness of stimuli, but it will not occur when subjects rate the bizarreness or interactiveness of stimuli. In addition, Kroll and his associates (Kroll, Jaeger, & Dornfest, 1992;Kroll, Schepeler, & Angin, 1986;Kroll & Tu, 1988) have documented a number of studies failing to achieve the bizarreness effect, and Riefer and Rouder (1992) achieved the effect in only two of three replications of the same experiment.This research was supported by NSF Grant SBR-9309667. The authors would like to thank Gil Einstein, Neal Kroll, and an anonymous reviewer for helpful comments on an earlier draft of the manuscript. Correspondence should be addressed to D. M. Riefer, Department of Psychology, California State University, San Bernardino, CA 92407 (e-mail: driefer@wiley.csusb.edu).Thus, the bizarreness effect continues to be a somewhat elusive phenomenon.In this article, we present a two-factor hypothesis...