This study is an attempt to contribute to previous research on the subject of data collection mode effects comparing specifically the Internet mode of data collection to telephone-based data collection. In this study, we controlled for sample source by having all interviews conducted with pre-recruited panelists from Knowledge Networks' web-enabled panel. The administered survey questions are the 'national priority' items from the General Social Survey and items on environmental policy attitudes. The GSS was in the field for the in-person main study during the fielding of our experiment. In the analysis, we compared the results from the two modes of data collection to identify categories of questions where the mode of data collection is related to a directional difference in the survey finding. The data collection took place in March-June 2006.