Neuroimaging studies have revealed an association between word generation and activity in the left inferior frontal gyrus (IFG) that is attentuated with item repetition. The experiment reported here examined the effects of repeated word generation, under conditions in which completion was either decreased or increased, on activity measured during whole-brain echoplanar functional magnetic resonance imaging. Activity in left IFG decreased during repetition conditions that reduced competition but increased during repetition conditions that increased competition; this pattern was contrasted to repetition effects observed in other cortical areas, specifically regions of left temporal cortex. The increase in left IFG activity, which is not predicted by a simple semantic retrieval account of prefrontal function, is consistent with the hypothesis that left IFG subserves the selection of semantic knowledge among competing alternatives.