Telephone surveys face more and more criticism because of decreasing coverage and increasing costs, and the risk of producing socially desirable answers. Consequently, survey administrators consider switching their surveys to the web mode, although the web mode is more susceptible to item nonresponse. Still, we do not know whether this is true for all question types. In this article, we analyze to what extent item nonresponse depends on question characteristics such as their form or difficulty in the telephone and the web mode. We use data from an experiment in which individuals randomly sampled from a population register are experimentally assigned to these two modes. Distinguishing effects on the frequency of don't know responses, item refusals, and mid-scale responding, we find more don't know responses and item refusals for the web mode generally, but no differences for mid-scale responding. However, this relationship depends on the characteristics of the question.