Event-related potentials were used to investigate if there is a lexical bias effect in comprehension monitoring. The lexical bias effect in language production (the tendency of phonological errors to result in existing words rather than nonwords) has been attributed to an internal self-monitoring system, which uses the comprehension system, and which employs lexical status as a monitoring criterion. It has been suggested that we monitor language comprehension too, and that the P600 reflects comprehension monitoring processes. If both production and comprehension monitoring rely on the comprehension system it is plausible that both processes are very similar. Hence the lexical bias effect is expected in comprehension monitoring. We presented high-cloze sentences that could contain a correct word, a lexical error, or a nonlexical error. There was a larger N400 in the lexical error and the nonlexical error conditions compared with the correct word condition. Importantly, the P600 was the largest in the nonlexical error condition, intermediate in the lexical error condition, and the smallest in the correct condition. Apparently, the comprehension monitor is sensitive to lexicality, suggesting that production and comprehension monitoring use similar criteria for error detection. (Contains 2 footnotes, 1 table, and 3 figures.)