Mismatch negativity, an index of automatic cerebral activity in response to novel stimuli, was used to determine the onset of morphosyntactic processing in French. Stimuli were four two-word sentences made up of a pronoun (first or second person) and a verb (first or second person). Verb forms differed only in the inflectional suffix, which made the sentences either syntactically correct or incorrect. The mismatch negativity response was found to be modulated by the grammaticality of the agreement relation at 50–140 ms after inflection onset, corroborating the previous finding that morphosyntactic processing occurs early and out of the focus of attention. The role of the pronoun–suffix association probabilities in determining the observed timing of morphosyntactic processing is discussed.