Web surveys offer new opportunities for achieving high-quality responses to open-ended questions because the interactive nature of the web allows questions to be tailored to individual respondents. This article explores how respondents' level of interest in the topic of the question can influence whether they provide a response and the quality of their answers. In addition, we examine whether an interactive follow-up probe, asked after people submit their initial response to the open-ended question, can improve the quality of responses. We find that respondents' interest in the question topic significantly affects the responses to open-ended questions, and interactively probing responses to open-ended questions in web surveys can improve the quality of responses for some respondents, particularly for those very interested in the question topic. Nonresponse remains a significant problem for open-ended questions; we found high item nonresponse rates for the initial question and even higher nonresponse to the probe, especially for those less interested in the topic of the question. Consequently, interactive probing should only be used for a few key open-ended questions within a survey where high-quality responses are essential and may be more effective for respondents who are already motivated to provide a response.