This study investigated the hypothesis that lexical representations are stored in morphologically decomposed form. Three lexical decision experiments in which the morphological structure of nonword stimuli was varied are reported. Systematic effects of morphological structure on reaction time and error performance were obtained. In particular, it was found that: (1) morphologically nondecomposable nonwords were easiest to process; (2) nonwords with partial morphological structure were processed with greater difficulty than this latter set of stimuli; and, (3) morphologically legal nonwords (i.e., nonwords that are exhaustively decomposable into morphemes) were processed with the greatest difficulty. Furthermore, it was found that within the class of morphologically legal nonwords performance was affected by the type of relationship that obtained between the morphemes that comprised a stimulus item. These results, which are interpreted as evidence in favor of the hypothesis that lexical representations are morphologically decomposed, are discussed in the context of the Augmented Addressed Morphology Model.