Lexical and syntactic processes are usually regarded as separate sub-systems of the language processing system. We re-examine the autonomy of these processes, given a mental lexicon that is morphemically decomposed, in 3 self-paced reading experiments. Although inflectional affixes have a syntactic role and derivational affixes have a lexical role, there were similar patterns of processing for both types of affix (Experiments 1 and 3). This suggests that there is a common combinatorial process at both levels of the system. Using novel and established morphologically complex words, we varied word-internal factors together with sentence level constraints (Experiment 2). Both sentence-level constraints and word-internal factors had parallel effects on the processing of novel and established words. Overall, the results indicate that the relationship between lexical and syntactic processing may be non-autonomous when morphological composition is taken into consideration.