In an effort to minimize respondent burden and survey costs and to improve response rates, mixed-mode data collection techniques are often used to collect information. With parallel data collection techniques, however, new methodological challenges are likely to emerge. In 2011, the Hungarian Central Statistical Office is about to collect census information from households and individuals using three data collection modes: selfadministered paper, self-administered online questionnaires and face-to-face interviews. Other studies have shown that choosing a data collection mode is usually not random; it is related to the characteristics of the respondent. Also, it is known that differences between information gathered by mode may originate from the technical features of the different questionnaires. In order to be prepared for the methodological challenges raised by this technique, a preliminary experimental study was undertaken to evaluate the presence of mode effects, using data collected in the 2009 census rehearsal. The paper describes the key points of the analysis – based on the Canadian 2006 internet mode effect study –, the data reported using the self-administered internet and paper questionnaires and face-to-face interviews, the different characteristics of the respondents and gives a summary and experiences on measuring mode effects.