Electrical scalp recordings revealed the brain's sensitivity to both lexical properties of words and their contextual fit with a previous sentence context around 400 ms after word presentation. The so-called N400 component has been suggested to reflect the cost either of target word recognition or of a postlexical process for integrating word meaning into a context. In a sentence comprehension study, we manipulated the potential interference exerted in visual word recognition by target words' orthographic neighbors and the semantic constraints induced by the context in one and the same experiment. Neighbor frequency modulated the N400 only in low-constraint contexts; in high-constraint contexts the largely suppressed N400 did not show this neighbor interference effect. Furthermore, the earlier onset of the ERP effect (about 100 ms) induced by the contextual manipulation compared to the neighbor manipulation suggests distinct neurocognitive processes affecting the N400 component in an interactive manner.