Does producing syntactic agreement rely on syntactic or memory-based retrieval processes? The present study investigated the extent to which syntactic processing deficits and working memory (WM) deficits predict susceptibility to agreement attraction (Bock & Miller, 1991), where speakers tend to erroneously produce plural agreement for a singular subject when another noun in the sentence is grammatically plural. Four brain-injured patients with varying degrees of grammatical and WM deficits completed sentences with local nouns that matched or mismatched in number with the head noun, and that were plausible or implausible subjects. Both aspects of grammatical deficits and the extent of WM deficits predicted the extent of agreement attraction effects. These data are consistent with the proposal that producing an agreeing verb involves a cue-based search in WM for an appropriate controlling noun, which is subject to interference from other elements in memory with similar properties (cf. Badecker & Kuminiak, 2007).