In several domains of psychology it has been shown that mood influences the way in which we process information. So far, little is known about the relation between mood and processes of language comprehension. In the present study we explore, whether, and if so how, mood affects the processing of syntactic anomalies in real time by recording event-related potentials (ERPs). To this aim we compared the P600 effect to subject-verb agreement errors relative to correct sentences while ERPs were recorded and mood was manipulated by presenting happy or sad film clips. The prediction was that if emotional state affects processes of language comprehension this should be reflected by an interaction between mood and P600. The results were as follows: first, the mood induction procedure was effective: participants were happier after watching happy film clips and sadder after watching sad film clips compared to baseline. Second, for P600 a mood by syntactic correctness interaction was obtained for the midline and lateral electrodes. The interaction reflected a broadly distributed P600 effect for the happy mood condition and a strong reduction in P600 effect for the sad mood condition. Correlation analyses confirmed that the observed changes in P600 effect were accompanied by reliable changes in emotional state. The present ERP findings demonstrate that mood interacts with processes of language comprehension. Three possible explanations for the mood by syntactic correctness interaction are discussed; one in terms of syntactic processing, one in terms of heuristic processing, and one in terms of more general factors like attention and/or motivation. (Contains 1 table and 7 figures.)