It sometimes happens that one is unable to recall a word or name that he feels he knows very well. This state of frustrated recall is referred to as a tip-of-the-tongue (TOT) experience. Two experiments were devised to compare the ability of a weak trace and a decoding-failure model to predict the conditions under which TOT reports would be most likely. A weak trace model asserts that TOTs will be more frequent when there is partial retrieval of the forgotten information or when easy items and good recallers are tested. A decoding failure model predicts instead that the TOT state represents the accessing of an undecodable retrieval plan and is more likely to occur for materials encoded by elaboration strategies than by rehearsal strategies. Analysis of feeling-of-knowing ratings and recall performance for elements in word matrices and for paired associates revealed that TOTs are more likely to be reported for elaboratively encoded stimuli and that this effect cannot be attributed to the increase in trace strength typically afforded by mnemonic strategies. These data suggest that it is the failure to decode an elaborated retrieval plan that generates the TOT experience. (Author)