It has been claimed that verb processing (as opposed to noun processing) is subserved by specific neural circuits in the left prefrontal cortex. In this study, we took advantage of the unusual grammatical characteristics of clitic pronouns in Italian (e.g., "lo" and "la" in "portalo" and "portala" "bring it [masculine]/[feminine]", respectively)--the fact that clitics have both nominal and verbal characteristics, to explore the neural correlates of verb and clitic processing. We used repetitive transcranial magnetic stimulation (rTMS) to suppress the excitability of the left prefrontal cortex and to assess its role in producing verb+det+noun and verb+clitic phrases. Results showed an interference effect for both kinds of phrases when stimulation was applied to the left but not to the right prefrontal cortex. However, the interference effect was significantly greater for the verb+clitic than for the verb+det+noun phrases. These findings support the view that clitics increase the morphosyntactic complexity of verbs.