This dissertation presents an experimental investigation of the representations of morphologically complex words with the intended goal of revealing how morphological information is realized in the mental lexicon. It focuses on the representations of prefixed words in English. Five segment shifting experiments (Feldman and Fowler 1987) and one speech error elicitation experiment (Baars and Motley 1976) are discussed. The results of these studies suggest that lexical representations of some prefixed words include associative links to their component morphemes while others include only weak associate links. Behavioral evidence for morphological complexity was dependent on the amount of linguistic evidence supporting complexity.