This article explores alternative designs for uncertain responses (i.e., "don’t know" or "no opinion" options) in a Web survey. In mail or other paper-based self-administered surveys, designers are forced to choose whether or not to provide an explicit uncertain response option. In interviewer-administered surveys, implicit uncertain responses are possible even when uncertain response options are not initially provided to a respondent; that is, when such a response is volunteered, it is accepted, often after an additional attempt to elicit a more definitive answer. Interactive Web-based surveys permit a design similar to interviewer-administered surveys. In an experiment, the authors examine several alternative design approaches to reducing the number of uncertain responses in a Web survey.