With this research we investigated the real-time electrophysiological correlates of noun-verb agreement checking during the comprehension of correct passive sentences in French. Event-related potentials were acquired while participants read passive sentences that contained covert (singular, masculine) or overt (plural, feminine) noun-verb agreement. Results show that the processing of overtly or covertly agreeing verbs in passive sentences is associated with an asymmetrical electrophysiological response, reflecting former psycholinguistic evidence of markedness and unmarkedness of certain features. The reading of an overtly marked verb agreeing in number and gender with a feminine plural subject was associated with a left anterior negativity (LAN), whereas covertly marked verbs were associated with a negativity presenting a central-posterior distribution, an N400. These results, confirming the lexical status of features and their immediate but asymmetrical checking during sentence comprehension are discussed in the context of current linguistic and psycholinguistic models of agreement checking. (C) 2007 Elsevier Ltd. All rights reserved.