This study uses event-related brain potentials (ERPs) to investigate the processing of morphologically regular and irregular words during auditory comprehension. ERPs were recorded, while 23 German-speaking subjects listened to correctly and incorrectly inflected noun plural forms presented in sentential contexts. ERP responses to violations of morphological structure were different to those of lexical (word-level) violations: the former elicited LAN/P600 effects, and the latter an enhanced N400 component relative to the correctly inflected plural forms. This difference replicates previous results from visual ERP studies and supports the distinction between combinatorial and memory-based processing of morphologically complex words. In addition, LAN/P600 effects were found to be more prominent in the auditory domain than in a previous visual study using similar materials.