Web surveys generally use some sort of access control in order to prevent uninvited respondents to take part in the survey, as well as to prevent multiple comple-tions by the same (invited) respondent. Restriction of survey access can be accom-plished in several technically equivalent ways. However, these methods may not be equivalent from a methodological viewpoint. In this paper, an exploration of possible effects of access control mechanisms is undertaken. Two different modes of access control were experimentally manipulated. Five hundred invited respon-dents were assigned to the automatic login condition. Another 500 respondents were assigned to the manual login condition. The respondents in the automatic lo-gin condition could sign in to the survey without having to key in their access code (a four digit PIN number), whereas respondents from the manual login condition did have to perform this action. It was expected that the automatic login procedure would generate higher response rates, but a lower degree of data quality. The data show that using a manual login procedure does not decrease response rates, and increases the overall degree of data quality. Respondents who logged in manu-ally tend to complete more questions, and generate more substantive answers to sensitive questions than respondents who logged in automatically.