The objective of the present study was to delineate brain-electrical correlates of semantic and syntactic integration processes during language comprehension. Twenty-eight subjects were engaged in a lexical decision task. The target item (a legal word or a pseudo word) was always preceded by a prime consisting of a sentence fragment that provided a particular context. With respect to the prime a word target could be either a correct completion, a violation of a semantic selection restriction, or a violation of a syntactic subcategorization rule. An N400-like wave was elicited by both types of deviations. Syntactic anomalies evoked a negative shift predominantly over the anterior scalp with a preponderance over the left hemisphere, while semantic anomalies were accompanied by a much more widespread negativity with the maximum over posterior temporal areas. The amplitude of the semantic vie lation effect was found to be related to the strength of the priming constraints. The topographic difference is consistent with the idea that syntactic and semantic aspects of comprehension are handled by different neural subsystems.