Three experiments are reported in which the word frequency effect is used as a diagnostic for determining whether affixed words coming from the same stem are stored together or separately in the lexicon. Prefixed words are examined in the first experiment, inflected words in the second and third. In the first two experiments, two types of word are compared where the words in each condition are matched on surface or presented frequency but are varied on the frequency of their stems or base frequency. It is found that lexical decision times are influenced by base frequency, thus indicating that words related by affixation are stored together in the lexicon. The third experiment, however, demonstrates that when base frequency is held constant and surface frequency is varied, lexical decision times are influenced by surface frequency. The results are accounted for by a model of word recognition whereby frequency has its effect at two different stages of the recognition process.In a paper by Taft and Forster (1975), evidenee was presented to support the view that visually presented prefixed words are analyzed into their separate morphemes [prefix and stern) when they are to be reeognized. For example, the reeognition of the word "unhook" would involve the stripping off of the prefix "un" and the subsequent loeation of the lexical entry for "hook." That is, "hook" and "unhook" would be aeeessed through the same lexical entry. The results obtained by Taft and Forster implied, furthermore, that a prefixed ward is aeeessed via its stern even when tbis stern is not a word in its own right (as "hook" is). For example, the prefixed word "persuade" would be reeognized after the prefix "per" was stripped off and the stern "suade" was loeated in the lexicon. Tbus, it is claimed that the nonword "suade" is stored in the lexicon for the purpose of recognizing "persuade." It would also be stored for the purpose of reeognizing "dissuade." Does this mean, then, that "persuade" and "dissuade" are aeeessed through the same lexical entry, "suade," or are there two separate entries for "suade"? This is the question that will be addressed in the first experiment to be reported.The idea bebind tbis experiment is similar to that of Rosenberg, Coyle, and Porter (1966), as well as Experiment 5 of Taft and Forster (1976). Rosenberg et al. employed a free reeal! task for lists of adverbs that were derived either from common adjectives (e.g., brightly) or uneommon adjectives (e.g., briskly). These two types of item were equated for frequeney of oeeurrenee of their adverbial forms, that is, the form in which the words were presented. It was found that the ease of recall of the adverbs was influeneed by the frequency of their adjectival sterns. Thus, "brightly" was presumably encoded in this episodic task as "bright ," and "briskly" as "brisk.".The frequency effect was similarly employed by Taft and Forster (1976), but this time, the task was a lexical one rather than an episodic one. In addition, compound words were examined rather than derived...