In this paper we describe the possibility to carry out clarification dialogues in the framework of the face-to-face translation system verbmobil. We focus on a special subtype of clarification dialogues which occur when the system has insufficient information to continue processing. The clarification dialogues currently incorporated in our system concern three aspects: (i) phonological ambiguities, (ii) unknown words, and (iii) semantic inconsistencies. We describe each of these subdialogues in detail and discuss the extensions and changes that had to be made to the overall system in order to allow for clarification dialogues. An outlook on future developments concludes the paper.