This paper is an examination of the interplay of mode of data collection and item nonresponse caused by 'Don't Know' responses. A series of experiments were carried out to replicate and extend earlier comparisons between an in-person survey (the General Social Survey) and Web-enabled Knowledge Networks surveys. Results indicate that levels of Don't Know on e-survey are highly contingent on format and conditioning effects and that a Web-based format for Don't Knows can be designed to match DK levels found in in-person surveys. Moreover, differences in distributions across modes are notably reduced with DK responses are excluded, but do not disappear. Support for public spending was generally greater on the in-person GSS than on the KN e-surveys and the differences were notable on items concerning the underclass. Finally, wording experiments produced results that were consistent in direction across modes, but not always comparable in magnitude. Thus, while e-surveys produce similar findings to in-person surveys in many circumstances, notable differences occur in other situations.