The increasing pressure for decreasing the costs of survey data collection has stimulated substantial interest in mode effects - the consequences of survey responses differing as the nature of data collection shifts from one mode to another. Over the past two decades, a large research literature that focuses on the impact of mode effects has emerged. This literature has focused predominantly on the nature of the changes (e.g., changes due to social desirability, changes due to extreme/moderate response styles) when the mode of data collection is changed. This paper focuses on respondent characteristics as causally related to the consequences of mode changes - that is, that some respondents are more susceptible, or sensitive, to mode changes, while the responses of others ore more resistant to mode effect changes. This research examines the first wave of data collected as part of the collaboration between the European Social Survey (ESS) and Gallup-Europe. This collaborative research effort focuses on the consequences of changing data collection mode for questions drown from the ESS and the Euro Barometer. The survey questions were selected for methodological reasons (e.g., complexity, social desirability) rather than for substantive content. The data, collected in Hungary during May and June of 2003, are from a fully-randomized, cross-over experimental design in which respondents were administered the same set of questions using two different data collection modes. All six combinations of four primary data collection modes - face-to-face, telephone, PAPI, and internet - are represented in the data. Preliminary analysis indicates that younger and more highly educated respondents appear to be the least susceptible (i.e., most resistant) to mode effects; older respondents and those with lower levels of education appear to be most sensitive to mode changes. ln addition, these indicators of cognitive ability also appear to be linked to the size of the mode effect.